;-NRLF 


E77    fllE 


INTRODUCTION 

TO 

ORGANIC    CHEMISTRY 


STODDARD 


INTRODUCTION 

TO 

ORGANIC  CHEMISTRY 


BY 

JOHN  TAPPAN  STODDARD 

PROFESSOR  OF  CHEMISTRY  IN  SMITH  COLLEGE 


SECOND  EDITION 


PHILADELPHIA 
P.   BLAKISTON'S  SON  &   CO. 

1012  WALNUT  STREET 


COPYRIGHT,  1918,  BY  P.  BLAKISTON'S  SON  &  Co. 


THE.  MAPLE-  PBJSBS.  YORK-  PA 


PREFACE  TO  THE  SECOND  EDITION 

The  favorable  reception  accorded  to  this  text  has  encouraged 
me  to  take  advantage  of  this  year's  reprinting  to  make  a  number 
of  corrections  and  changes  that  have  been  suggested  during  the 
four  years  since  it  first  appeared. 

Many  minor  alterations  will  be  found,  and  a  few  portions  have 
been  entirely  rewritten.  Among  the  latter  are  the  sections  on 
the  Natural  Oils  and  Fats,  on  Uric  Acid  and  the  Purine  Bases, 
and  on  the  Proteins. 

I  trust  that  the  revision  will  be  found  to  have  measurably 
improved  the  book  and  that  its  efficiency  as  an  aid  to  the  instruc- 
tion of  college  students  who  are  beginning  the  subject  has  been 
increased. 

It  gives  me  great  pleasure  to  acknowledge  my  indebtedness 
to  the  friends  whose  criticisms  and  suggestions  have  aided  me 
in  my  task,  and  I  am  under  especial  obligation  to  Professor 
Cook  of  Smith  College  and  Dr.  Harry  L.  Fisher  of  Columbia 
University  who  placed  in  my  hands  the  corrections  and  notes 
they  had  mlade  while  using  the  book  with  their  classes. 

J.  T.  S. 

NORTHAMPTON,  MASS. 


574256 


PREFACE  TO  THE  FIRST  EDITION 

This  book  is  intended  to  be  used  in  connection  with  lectures, 
recitations,  and  laboratory  work  in  the  first  course  of  Organic 
Chemistry  in  college.  The  author  has  endeavored  to  present  the 
subject  simply,  directly,  and  connectedly,  so  that  the  student 
may  gain  a  clear  idea  of  the  principles  of  organic  chemistry  and 
its  relations  to  general  chemistry.  The  fundamentally  important 
questions  of  the  constitution  of  organic  compounds  are  discussed 
at  some  length  in  many  typical  cases.  In  these  discussions,  the 
facts  in  regard  to  the  behavior  of  the  substances  are  given  first, 
and  then  the  arguments  by  which  the  formulas  are  established. 
The  student  in  this  way  is  trained  in  the  method  of  deriving 
constitutional  formulas,  and  should  soon  be  able  to  work  out 
simple  problems  from  a  given  statement  of  facts.  Emphasis  is 
laid  on  general  reactions  and  characteristics,  rather  than  on  special 
facts  relating  to  particular  compounds;  and  the  text  is  relieved 
from  much  detail  by  the  use  of  tables  giving  names,  formulas  and 
properties  of  many  groups  of  compounds.  Many  applications 
of  organic  chemistry  to  practical  life  are  given  so  that  the  student 
may  realize,  in  some  measure,  the  part  which  the  science  of 
organic  chemistry  plays  in  ordinary  life  and  in  our  industries. 

The  book  is  considerably  smaller  than  many  of  the  text-books 
on  the  subject,  but  it  is  believed  that  it  is  none  the  less  complete 
in  all  the  essential  matter  which  is  properly  presented  in  a  first 
course.  The  larger  text-book  is  apt  to  bewilder  the  student  by 
brief  descriptions  of  too  many  compounds  of  minor  importance, 
or  to  fill  too  many  pages  with  discussions  which  can  be  conducted 
to  better  advantage  by  the  lecturer. 

The  student  often  finds  his  course  in  organic  chemistry  at 

vii 


Vlll  PREFACE 

first  difficult  and  confusing.  It  is  so  different  from  the  inor- 
ganic chemistry  that  it  takes  him  some  time  to  get  the  new 
point  of  view.  This  is,  perhaps,  to  some  extent  inevitable;  but 
a  good  deal  depends  on  the  manner  in  which  the  subject  is  intro- 
duced. If  details  are  subordinated  and  the  fundamental  princi- 
ples are  presented  logically  and  with  a  f  ew  well-chosen  illustrations 
of  their  applications,  the  first  difficulties  are  soon  overcome. 

The  order  in  which  the  various  groups  of  compounds  are  to  be 
treated  is  a  more  or  less  open  question.  The  choice  depends 
largely,  in  several  instances,  on  the  particular  relations  which  it 
seems  desirable  to  emphasize.  What  appears  a  logical  sequence 
from  one  point  of  view,  is,  from  another,  illogical.  No  claim  is 
made  that  the  order  given  in  this  book  is  the  best;  and  it  should 
be  said  that  it  is  not  necessary  that  this  order  be  strictly  followed 
by  those  who  use  the  book. 

Numerous  cross-references  are  given  to  help  in  binding  the 
discussions  into  a  coherent  whole.  Some  references  are  made  to 
books  in  which  fuller  treatment  of  certain  subjects  will  be  found, 
and  a  short  list  of  books  for  collateral  reading  is  given  at  the  end 
of  the  volume. 

I  wish  to  express  my  sincere  thanks  to  Professor  H.  W. 
Doughty  of  Amherst  College  and  Professor  E.  P.  Cook  of  Smith 
College,  who  have  read  the  book  in  manuscript  and  have  made 
many  helpful  suggestions.  Professor  Cook  has  also  rendered 
great  assistance  in  reading  the  proofs. 


CONTENTS 

CHAPTER  PAGE 

I.  PRELIMINARY  DISCUSSION i 

II.  THE  PARAFFINS  OR  HYDROCARBONS  OF  THE  METHANE 

SERIES «,     .  15 

III.  HALOGEN  SUBSTITUTION  PRODUCTS  OF  THE  PARAFFINS     .  31 

IV.  UNSATURATED  HYDROCARBONS 42 

V.  THE  ALCOHOLS 57 

VI.  THE  ETHERS ,     .  70 

VII.  ALDEHYDES  AND  KETONES 76 

VIII.  SIMPLE  MONOBASIC  ACIDS 94 

IX.  ACID  CHLORIDES — ANHYDRIDES — ESTERS 114 

X.  AMINES  AND  AMIDES — NITRO-COMPOUNDS       .     .     .     .  127 

XI.  CYANOGEN  AND  CYANOGEN  COMPOUNDS 144 

XII.    POLYHYDROXYL  ALCOHOLS 155 

XIII.  OXIDATION  DERIVATIVES  OF  POLYHYDROXYL  ALCOHOLS 

— STEREOCHEMISTRY 161 

XIV.  POLYBASIC  ACIDS  AND  ALCOHOL-ACIDS 177 

XV.  CARBOHYDRATES — FERMENTATION — ENZYMES      .     .     .  198 

XVI.  DERIVATIVES  OF  CARBONIC  ACID 227 

XVII.  COMPOUNDS  CONTAINING  SULPHUR 236 

XVIII.  SOME  HALOGEN  AND  AMINO  DERIVATIVES       ....  245 

XIX.  CYCLO-PARAFFINS 257 

XX.  AROMATIC  HYDROCARBONS — ORIENTATION      ....  265 
XXI.  HALOGEN  DERIVATIVES — SULPHONIC  ACIDS — NITRO-COM- 
POUNDS— INFLUENCE  OF  SUBSTITUENTS  ON  EACH  OTHER.  284 

XXII.  AROMATIC  AMINES 301 

ix 


X  CONTENTS 

CHAPTER  PAGE 

XXIII.  DIAZO  COMPOUNDS .     313 

XXIV.  Azo  AND  OTHER  NITROGEN  COMPOUNDS — DYES  .      .      .321 
XXV.  PHENOLS — AROMATIC  ETHERS — ALCOHOLS      .     .     .      .327 

XXVI.  AROMATIC  ALDEHYDES — KETONES  AND  QUINONES     .     .  343 

XXVII.  AROMATIC  ACIDS 353 

XXVIII.  HYDROAROMATIC  HYDROCARBONS  AND  THEIR  DERIVA- 
TIVES— TERPENES  AND  CAMPHORS 371 

XXIX.  NAPHTHALENE  AND  ANTHRACENE    .      .      .     ...     .      .  382 

XXX.  HETEROCYCLIC  COMPOUNDS 393 

XXXI.  ALKALOIDS — PROTEINS    .     ' 402 

INDEX 413 


TABLES 

PAGE 

ACIDS,  AROMATIC 356 

DIBASIC i77 

HYDROXY  (ALIPHATIC) 197 

HYDROXY  (AROMATIC) 363 

MONOBASIC  (NORMAL) 101 

SULPHONIC 292 

ACID  AMIDES 142 

ANHYDRIDES 117 

CHLORIDES 117 

ALCOHOLS,  AMYL     68 

PRIMARY 67 

ALDEHYDES 87 

AMINES,  ALKYL 136 

AROMATIC      312 

CYCLO-PARAFFINS 258 

ESTERS  OF  INORGANIC  ACIDS 122 

ETHERS     75 

ETHYL  ESTERS  OF  ORGANIC  ACIDS 123 

HYDROCARBONS,  AROMATIC 276 

UNSATURATED      45 

IONIZATION  CONSTANTS      407 

KETONES 88 

NITRO  COMPOUNDS  (AROMATIC) 297 

PARAFFINS,  NORMAL 17 

HALOGEN  DERIVATIVES 33, 40 

PHENOLS 331 

SPECIFIC  ROTATIONS 406 


XI 


INTRODUCTION   TO    ORGANIC 
CHEMISTRY 


CHAPTER  I 
PRELIMINARY    DISCUSSION 

Organic  chemistry  is  the  chemistry  of  the  compounds  of  carbon. 
Although  the  fundamental  laws  and  theories  of  chemistry  are  as 
applicable  to  these  compounds  as  to  all  others,  there  are  several 
reasons  for  their  separate  treatment. 

In  the  first  place,  the  number  of  compounds  that  contain  carbon  j 
is  extraordinarily  large.  The  only  other  elements  that  enter  into 
the  composition  of  any  very  large  number  of  substances  are 
hydrogen  and  oxygen;  and  we  shall  see  that  hydrogen  and  oxygen 
are  quite  usually  associated  with  carbon  in  the  organic  compounds. 
The  association,  however,  is  of  such  a  nature  that  carbon  is  the 
dominant  element,  so  to  speak,  remaining  intact  in  very  many  of 
the  chemical  changes  that  occur,  while  hydrogen  and  oxygen  are 
added,  subtracted,  or  exchanged  for  other  elements  or  groups  of 
elements.  The  great  number  and  variety  of  the  compounds  in 
which  carbon  is  a  constituent  is  of  itself  a  sufficient  ground  for 
making  their  discussion  a  separate  branch  of  study. 

In  the  second  place,  there  are  certain  general  characteristics 
which  distinguish  the  organic  substances  from  the  inorganic. 
Most  of  the  compounds  of  carbon  are  decomposed  at  temperatures  / 
which  are  below  a  red  heat,  while  many  inorganic  compounds  with- 
stand much  higher  temperatures;  and  organic  compounds  are 
more  liable  to  change  when  exposed  to  the  light  and  air  than  are  « 

i 


INTRODUCTION  (TO    ORGANIC    CHEMISTRY 

the  inorganic.  The  majority  of  organic  substances  are  practically 
insoluble  in  water,  which  is  the  solvent  of  so  many  inorganic 
compounds,  and  are  usually  soluble  in  such  liquids  as  ether, 
chloroform,  alcohol,  carbon  disulphide,  and  benzene,  in  which  few 
of  the  inorganic  compounds  dissolve. 

Again,  while  the  greater  number  of  inorganic  compounds 
*  with  which  we  deal  in  aqueous  solution  react  almost  instan- 
taneously with  each  other,  if  at  all,  the  reactions  between  dissolved 
or  liquid  organic  compounds,  though  occasionally  rapid,  are  more 
frequently  very  slow,  often  requiring  heat,  and  hours  or  even  days 
for  completion.  This  difference  in  behavior  is  explained  by  the 
fact  that  the  inorganic  compounds  are  electrolytes  and  the 
reactions  are  the  rea£liojas__of_ians,  while  comparatively  few 
organic  compounds  are  ionized,  and  their  reactions  are  those  of 
undissocjaleji^mjolecules. 

These  distinctions  must  not  be  understood  to  be  absolute. 
Some  carbon  compounds,  such  as  the  carbides  of  the  metals,  the 
oxides  of  carbon,  and  others  withstand  very  high  temperatures, 
while  a  considerable  number  of  inorganic  compounds  are  decom- 
posed at  a  moderate  heat;  and  a  number  of  organic  substances 
dissolve  in  water  and  are  electrolytes,  while  some  inorganic 
compounds  dissolve  in  the  non-aqueous  solvents  which  were 
named,  and  usually  without  ionization.  The  differences,  however, 
are  sufficiently  general  to  justify  the  separate  treatment. 

Another  peculiarity  of  organic  substances  is  that  among  them 
we  find  many  large  groups  of  closely  related  substances — the 
relation  being  much  closer  than  that  which  exists  between  the 
members  of  the  inorganic  classes  of  bases,  acids  and  salts.  The 
members  of  each  of  these  organic  groups  not  only  give  similar 
reactions  with  a  given  reagent,  yielding  similar  products,  but 
show  a  nearly  uniform  gradation  in  all  their  physical  and  chemical 
properties.  This  very  much  simplifies  our  study;  for  when  we 
have  learned  the  characteristics  of  one  or  two  members  of  a  group, 
detailed  examination  of  the  others  becomes  unnecessary. 


PRELIMINARY    DISCUSSION  3 

A  complete  discussion  of  the  compounds  of  carbon  would  include 
carbon  monoxide,  carbon  dioxide,  carbon  disulphide,  certain 
carbides,  carbonic  acid,  and  the  carbonates — substances  which 
are  usually  treated  in  inorganic  chemistry  on  account  of  their 
close  relations  to  inorganic  compounds.  All  of  these  compounds, 
however,  have  also  certain  relations  to  other  compounds  of  carbon, 
so  that  some  reference  to  them  which  will  bring  out  this  relation 
should  be  made  in  organic  chemistry. 

Sources  of  Organic  Compounds. — Carbon  combines  directly 
with  hydrogen  at  high  temperatures,  and  the  hydrocarbons  which 
are  formed  may  be  employed  as  the  starting  point  for  the  prepara- 
tion of  a  great  variety  of  other  organic  compounds.  Some  simple 
organic  substances  may  be  made  by  the  use  of  the  oxides  of  car- 
bon, its  sulphide,  chloride,  and  one  or  two  carbides  of  the  metals, 
and  these  may  then  be  built  up  into  more  complex  compounds 
by  laboratory  methods.  But  in  actual  practice  the  chief  sources 
of  organic  compounds  are  in  the  products  elaborated  in  plants 
and  animals.  These  substances  were  the  first  to  receive  the  name 
"organic,"  and  for  a  long  time  it  was  believed  impossible  to  pro- 
duce any  of  them  artificially  from  the  elements  or  from  so-called 
inorganic  material.  Among  the  important  organic  compounds 
which  are  found  already  formed  in  plants  are  starch,  cellulose, 
the  sugars;  acids  or  salts  of  acids,  such  as  oxalic,  citric,  tartaric 
acids;  the  alkaloids,  such  as  quinine  and  strychnine,  and  many 
other  substances  of  greater  or  less  complexity.  Petroleum  con- 
tains many  compounds  of  carbon  and  hydrogen.  Many  organic 
substances  are  also  produced  by  the  destructive  distillation  of 
coal,  wood,  and  bones — those  which  are  contained  in  the  coal  tar 
being  of  the  greatest  interest  and  practical  value.  Furthermore, 
fermentative  processes  produce  ordinary  alcohol  from  sugar, 
acetic  acid  from  alcohol,  and  a  number  of  other  compounds. 

It  is  interesting  to  note  that  we  may  trace  the  source  of  the 
natural  organic  substances  to  the  carbon  dioxide  of  the  air,  which, 
in  turn,  is  supplied  to  the  air  by  the  combustion,  decay,  fermenta- 


4  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

tion,  etc.,  of  plant  and  animal  matter.  All  of  the  carbon  in 
plants — and  it  is  the  chief  element  they  contain — is  derived  from 
this  gas  which  forms  only  about  three  ten-thousandths  of  the  vol- 
ume of  the  air.  Under  the  influence  of  solar  energy,  carbon 
dioxide,  water,  and  small  quantities  of  other  simple  inorganic  com- 
pounds taken  up  through  the  roots  from  the  soil,  are  built  up  into 
the  structure  of  the  plant  or  vegetable,  oxygen  being  returned  to 
the  air.  The  chemical  processes  in  the  growing  plant  are,  in  gen- 
eral, of  a  synthetic  character,  and  "  endothermic  "  or  such  as  require 
the  expenditure  of  energy  (furnished  by  the  sun)  to  produce  them. 
But  at  the  same  time,  processes  of  the  opposite  character,  or 
analytic  processes  which  are  "  exothermic, "  go  on  to  some  extent, 
as  is  shown  by  the  fact  that  plants  exhale  carbon  dioxide.  Since 
the  food  of  animals  is  either  directly  or  indirectly  of  vegetable 
origin,  the  compounds  which  are  formed  in  their  bodies  owe  their 
principal  constituent,  carbon,  to  the  same  original  source.  But 
the  chemical  changes  in  the  living  animal  are  more  largely  of 
an  analytic  character  than  those  in  the  growing  plant.  While 
new  complex  substances  are  built  up  from  the  food  materials,  the 
resolution  of  these  into  simpler  compounds  is  all  the  time  proceed- 
ing. These  latter  reactions,  being  exothermic,  supply  the  energy 
which  maintains  the  temperature  and  varied  activities  of  the 
animal  body. 

In  the  greater  number  of  these  natural  substances  and  in  those 
directly  obtained  from  them  in  the  ways  which  have  been  men- 
tioned, we  find  only  three  elements  beside  carbon,  viz.,  hydrogen, 
oxygen,  and  nitrogen.  Many  contain  only  carbon  and  hydrogen; 
a  large  number,  carbon,  hydrogen  and  oxygen;  and  a  compara- 
tively small  number,  carbon  and  nitrogen  with  either  hydrogen, 
or  both  hydrogen  and  oxygen.  A  still  smaller  number  of  definite 
organic  compounds  containing  sulphur  or  phosphorus  are  found 
in  nature,  and  certain  metals — chiefly  potassium,  sodium,  and  cal- 
cium— are  present  in  the  natural  salts  of  organic  acids. 

While  the  number  of  elements  that  enter  into  the  composition 


PRELIMINARY   DISCUSSION  5 

of  the  natural  organic  compounds  is  thus  limited,  many  other 
elements  may  be  introduced  by  laboratory  methods.  The  chem- 
ist has  by  no  means  succeeded  in  making  in  his  laboratory  all  the 
organic  compounds  which  are  found  in  nature,  and  where  he  has 
succeeded,  it  is  very  seldom  that  the  steps  of  his  processes  are 
those  followed  by  nature.  Natural  compounds  are  formed  in 
living  organisms  at  ordinary  temperatures,  while  the  laboratory 
products  are  usually  obtained  by  the  use  of  higher  temperatures 
and  under  other  conditions  quite  dissimilar  to  those  which  prevail 
in  the  plant  or  animal. 

The  immense  number  of  compounds  which  carbon  forms  with 
four  or  five  other  elements  must  mean  that  the  molecules  of  many 
of  them  are  of  great  complexity;  and  in  fact  the  evidence  indicates 
that  the  carbon  atoms  possess  the  unusual  property  of  combining 
with  each  other  in  what  we  picture  to  be  chains  or  rings  of  atoms 
united  by  one  or  more  of  their  valencies,  while  the  remaining 
valencies  serve  to  hold  the  other  elements  of  the  compound.  Not 
only  is  this  the  case,  but  a  given  number  of  atoms  of  carbon  and 
of  one  or  two  other  elements  often  combine  in  varied  relations, 
giving  compounds  of  distinct  properties.  The  molecules  of  such 
compounds  of  the  same  composition  but  different  properties  may 
be  regarded  as  analogous  to  the  patterns  which  may  be  made  by 
putting  together  a  definite  number  of  colored  or  differently  shaped 
blocks  in  various  ways;  and  indeed  the  graphic  formulas  which 
the  organic  chemist  uses  to  explain  the  variety  he  finds  resemble 
such  patterns  with  the  atomic  symbols  used  instead  of  blocks. 
It  is  thus  seen  that  valency  and  the  combinations  which  it  per- 
mits must  play  an  immensely  greater  part  in  the  discussions 
of  organic  chemistry  than  it  usually  does  in  those  of  inorganic 
compounds. 

Identification  of  a  Substance  as  Organic. — This  resolves  itself 
into  a  test  for  carbon.  Most  organic  substances  burn,  and  if 
the  substance  chars  or  if  the  flame  deposits  lampblack  on  a  cold 


6  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

surface  which  is  brought  into  it,  no  further  test  is  necessary. 
Many  organic  compounds  show  the  presence  of  carbon  by  charring 
when  heated  in  an  ignition  tube;  but  the  most  general  test  for 
carbon  is  the  formation  of  carbon  dioxide  and  its  detection  by 
lime  water.  The  substance  is  heated  with  copper  oxide  in  a  test 
tube  and  any  gases  that  are  formed  are  led  into  lime  water;  or 
if  the  substance  is  a  gas,  or  one  which  sublimes  or  distils  before 
reacting  with  the  copper  oxide,  its  vapor  is  led  through  a  tube 
containing  hot  copper  oxide. 

Test  for  Elements  Combined  with  Carbon. — Hydrogen  is  usu- 
ally indicated  by  the  water  produced  in  the  test  for  carbon;  but, 
as  practically  all  organic  substances  contain  hydrogen,  a  test 
for  this  element  is  seldom  necessary  • 

Nitrogen. — If,  in  the  burning  or  charring  of  the  substance,  an 
odor  like  that  of  burning  wool  is  noticed,  this  shows  that  nitrogen 
is  a  constituent  of  the  substance.  Many  organic  compounds, 
however,  which  contain  nitrogen  do  not  give  this  odor.  In  this 
case,  the  substance  is  ignited  with  sodium  (or  with  a  mixture  of 
magnesium  powder  and  sodium  carbonate)  in  a  test  tube,  and  if 
nitrogen  is  present  it  forms  a  cyanide,  which,  when  brought  into 
solution,  and  digested  with  a  few  drops  of  a  mixture  of  ferrous 
and  ferric  salts,  gives  a  precipitate  of  Prussian  blue  when  acidu- 
lated with  hydrochloric  acid.  Certain  substances  which  contain 
nitrogen  fail,  however,  to  give  this  test,  since  the  nitrogen  is  dis- 
engaged as  gas  at  a  temperature  below  that  at  which  the  reaction 
with  the  metal  occurs.  In  these  cases  it  is  necessary  to  prove 
that  nitrogen  is  one  of  the  gases  evolved  when  the  substance  is 
heated,  or  when  it  is  oxidized  as  in  the  quantitative  determina- 
tion of  nitrogen.  The  other  elements  which  may  be  present, 
such  as  sulphur,  phosphorus,  and  the  halogens,  may  be  detected 
in  the  soluble  product  formed  by  the  ignition  of  the  substance  with 
sodium,  where  they  appear  as  sodium  compounds  and  respond 
to  the  usual  tests  of  inorganic  chemistry.  Halogens  may  be 
detected  more  simply  by  bringing  a  bit  of  the  substance  on  a  clean 


PRELIMINARY   DISCUSSION  7 

copper  wire  into  the  Bunsen  flame;  if  a  halogen  is  present  it  forms  a 
volatile  copper  halide  which  colors  the  flame  green.  Or  the  sub- 
stance may  be  ignited  with  calcium  oxide,  when  the  calcium  halide 
is  produced  together  with  the  carbonate,  and  after  dissolving  in 
dilute  nitric  acid  the  halogen  is  detected  by  adding  silver  nitrate. 
Metals  which  may  be  present  are  detected  in  the  residue  from 
ignition  by  the  usual  procedure  of  qualitative  analysis. 

Tests  for  Purity. — Before  the  quantitative  composition  of  a 
compound  can  be  determined,  it  is,  of  course,  necessary  to  obtain 
it  in  a  state  of  purity.  The  usual  tests  for  the  purity  of  solid 
and  liquid  organic  compounds  are  the  melting  and  the  boiling 
points.  If  a  solid  melts  abruptly  at  a  certain  temperature  (01 
witEin  a  range  of  0.5°)  it  is  considered  pure  enough  for  most 
purposes.  Impurities  cause  a  more  gradual  melting,  and  at  a 
temperature  which  is  lower  than  that  of  the  pure  substance. 
Pure  liquids  have  a  constant  boiling  point,  while  in  the  case  of 
mixtures  the  temperature  generally  rises  as  the  distillation  pro- 
ceeds. There  are,  however,  some  mixtures  of  definite  composi- 
tion, such  as  alcohol  and  water,  which  have  a  constant  boiling 
point  under  a  given  pressure.  A  change  of  pressure  (distillation 
in  a  partial  vacuum)  reveals  their  character,  for  while  the  boiling 
point  of  a  pure  substance  would  still  be  constant,  though  different, 
under  the  new  pressure,  the  boiling  point  of  the  mixture  becomes 
inconstant  until  a  new  equilibrium  is  established  with  a  different 
proportion  of  the  components.1 

Methods  of  Purification. — The  general  method  for  the  purifica- 
tion of  solid  organic  compounds  is  by  fractional  crystallization 
from  an  appropriate  solvent.  Organic  liquids  are  purified  by 
fractional  distillation,  the  distillate  being  collected  in  sepa- 
rate portions  or  "fractions"  for  small  ranges  of  temperature  as 
shown  by  a  thermometer  suspended -in  the  vapor.  A  partial 

1  Refer  to  the  behavior  of  mixtures  of  hydrochloric  and  of  nitric  acids  with 
water.  For  a  discussion  of  the  boiling  points  of  mixtures  see  some  Physical 
Chemistry. 


8  INTRODUCTION    TO    ORGANIC    CHEMISTRY 

separation  of  the  constituent  liquids  is  effected  in  this  way,  and 
the  separation  is  made  more  complete  by  redistilling  the  fractions 
a  sufficient  number  of  times.  When  the  substance  is  one  which 
decomposes  at  or  below  its  boiling  point  under  ordinary  atmos- 
pheric pressures,  it  may  be  distilled  at  a  lower  temperature  with- 
out decomposition  in  a  partial  vacuum,  (e.g.,  in  the  preparation 
of  glycerine).  A  method  which  is  successful  in  a  number  of 
instances  is  by  distillation'  in  a  current  of  steam,  as  in  the 
preparation  of  aniline  and  nitrobenzene.  Mixtures  of  solids  or 
of  liquids  can  frequently  be  separated  into  the  individual  con- 
stituents, or  one  constituent  can  be  extracted  in  a  state  of 
purity,  by  taking  advantage  of  the  different  solubilities  in  various 
solvents.  A  pure  solid  compound  may  sometimes  be  obtained 
from  a  mixture  by  sublimation  (cf.  benzoic  acid). 

No  general  methods  are  known  for  the  purification  of  gases. 
Most  frequently  it  is  effected  by  absorbing  one  or  more  of  the 
constituents  of  the  mixture  in  certain  liquids  or  solids.  But  usu- 
ally it  is  necessary  to  prepare  the  gas  as  pure  as  possible  from 
pure  materials  by  a  definite  chemical  action.  Even  then,  in  most 
cases,  there  are  impurities  of  small  amount  which  must  be  removed 
by  absorption  in  some  substance. 

Quantitative  Analysis. — Carbon  and  hydrogen  are  always 
determined  in  one  operation,  which  consists  in  the  complete 
oxidation  of  a  weighed  portion  of  the  pure  compound  (usually 
by  means  of  copper  oxide)  and  absorbing  the  water  in  solid 
calcium  chloride,  and  the  carbon  dioxide  in  a  strong  solution  of 
potassium  hydroxide.  From  the  increase  in  weight  of  these  sub- 
stances, the  amounts  of  hydrogen  and  carbon  are  calculated.  The 
weight  of  the  nitrogen  may  be  determined  (by  the  Dumas  method) 
from  the  volume  of  gas  collected  over  potassium  hydroxide  solu- 
tion when  the  substance  is  oxidized  by  copper  oxide  in  an  appara- 
tus from  which  the  air  has  been  displaced  by  carbon  dioxide. 
This  is  often  called  the  " absolute  method."  By  the  method  of 
Kjeldahl,  which  is  the  one  generally  used  in  the  analysis  of  foods 


PRELIMINARY   DISCUSSION  9 

and  other  complex  mixtures,  the  nitrogen  is  converted  into  am- 
monium sulphate  by  heating  the  substance  with  concentrated 
sulphuric  acid,  and  from  this  compound  ammonia  is  set  free  by 
sodium  hydroxide  and  absorbed  in  a  measured  quantity  of  stand- 
ard acid.  The  amount  of  acid  neutralized  by  the  ammonia  is 
determined  by  titration,  and  from  these  figures  the  amount  of 
ammonia  and  hence  of  nitrogen  is  readily  calculated.  No  satis- 
factory method  for  the  direct  determination  of  oxygen  has  been 
found,  and  the  percentage  of  this  element  is  usually  estimated 
by  subtracting  the  sum  of  the  percentages  found  for  the  other 
elements  from  one  hundred. 

For  the  determination  of  sulphur  or  phosphorus,  the  substance 
is  oxidized — usually  by  heating  with  fuming  nitric  acid  in  a 
sealed  tube — so  that  these  elements  are  converted  into  sulphuric 
or  phosphoric  acid,  from  which  the  amount  of  each  is  found  by  the 
ordinary  methods  of  inorganic  quantitative  analysis.  The  halo- 
gens are  determined  as  silver  halides,  being  converted  into  this 
form  by  oxidizing  the  substance  as  above  in  the  presence  of  silver 
nitrate. 

If  metals  are  present  in  organic  compounds,  as  in  the  case  of 
organic  salts,  it  is  usually  sufficient  to  ignite  a  weighed  amount  of 
the  substance,  when  the  carbonate  or  oxide  of  the  metal  is  left,  and 
can  be  weighed  as  such,  or  the  metal  determined  in  the  usual 
ways.  Such  metals  as  silver  and  platinum  are,  of  course,  left 
from  the  ignition  in  the  metallic  state. 

The  Empirical  Formula. — Since  the  empirical  formula  of  a 
compound  is  simply  a  record  of  the  quantitative  composition  in 
terms  of  atomic  weight  units,  it  is  found  by  translating  the  parts 
by  weight,  or  the  percentages  obtained  from  the  quantitative 
analysis,  into  these  terms.  The  student  is  familiar  with  the 
method  from  his  work  in  inorganic  chemistry.  The  symbol  of  an 
element  represents  a  definite  number  of  atomic  weight  units,  and 
the  relative  numbers  of  atoms  of  the  several  elements  that  make  up 
the  compound  are  found  by  dividing  the  percentages  or  proper- 


10  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

tional  weights  of  the  elements  by  their  respective  atomic  weights. 
The  quotients  thus  obtained  are  compared,  and  their  ratios  to 
each  other  expressed  in  the  smallest  whole  numbers.  For  in- 
stance: A  certain  compound  is  found  to  have  the  following  per- 
centage composition:  C  =  40.00,  H  =  6.67,  O  =  53.33, 

40.00-5-12=3.33 

6.67  -5-     I  =  6.67 

53-33  -M6  =  3-33 

Therefore  the  composition  in  atomic  weight  units  is  most  simply 
expressed  in  the  formula  CH2O.  Since  the  methods  of  quanti- 
tative analysis  are  always  subject  to  small  errors,  the  ratios  of  the 
quotients  often  cannot  be  expressed  in  exact  whole  numbers;  in 
these  cases,  the  values  which  are  the  nearest  possible  to  whole 
numbers  are  taken  as  representing  those  numbers. 

Molecular  Formulas.— Since  the  empirical  formula  is  merely  an 
expression  in  chemical  notation  of  the  quantitative  composition, 
any  formula  which  is  the  multiple  of  the  simplest  one  would  express 
this  fact  with  the  same  accuracy.  Now  it  happens  very  often 
in  organic  chemistry  that  there  are  two  or  more  distinct  com- 
pounds of  different  properties  which  have  the  same  percentage 
composition,  and  consequently  the  same  empiricial  formula. 
There  are,  for  example,  several  different  compounds  which  have 
the  same  composition  and  hence  the  same  empirical  formula  as 
that  taken  for  illustration  above.  This  fact  suggests  that  the 
molecules  of  these  compounds  are  probably  of  different  weights, 
and  that  while  one  of  them  may  be  properly  represented  by  the 
formula  CH2O,  the  others  have  such  formulas  as:  C2H4O2, 
C3H6O3,  C4H8O4,  C6Hi2O6,  etc.  We  must,  therefore,  find  the 
molecular  weight  of  the  compound  in  order  to  decide  which  of  the 
possible  multiple  formulas  belongs  to  it. 

The  student  probably  remembers  the  relation  between  the 
densities  of  gases  or  vapors  and  molecular  weights:  By  the  hy- 
pothesis of  Avogadro,  equal  volumes  of  all  gases,  when  measured 


PRELIMINARY  DISCUSSION  II 

under  the  same  conditions  of  temperature  and  pressure,  contain 
equal  numbers  of  molecules.  It  follows  that  since  density  is 
the  weight  of  a  unit  volume,  the  molecular  weight  of  a  gas  or 
vapor  can  be  found  by  comparing  its  density  with  the  density  of 
some  gas  whose  molecular  weight  is  known,  such  as  hydrogen 
(2),  oxygen  (32),  or  air  (whose  average  molecular  weight  is 
28.96).  This  method  can  be  employed  only  with  substances" 
which  are  gases,  or  are  converted  into  vapor  without  decomposi- 
tion. The  densities  of  gases  and  of  vapors  can  be  determined 
by  direct  or  indirect  weighing,  and  measuring  the  volume.  The 
vapor  densities  of  volatile  liquids  or  solids  are  usually  found  by  the 
method  of  Victor  Meyer,  which  consists  in  causing  the  vapor  from 
a  known  weight  of  substance,  formed  suddenly  at  a  temperature 
much  above  its  boiling  point,  to  displace  its  own  volume  of  air. 
The  apparatus  is  arranged  so  that  this  air  is  collected  over  water 
and  measured  at  room  temperature.  By  this  method  the  molecu- 
lar weight  of  one  of  the  compounds  whose  empirical  formula  is 
CH2O  is  found  to  be  30;  hence  the  molecular  formula  is  at  once 
picked  out  from  the  possible  multiples  as  CH2O,  since  here  the 
sum  of  the  atomic  weights  is  30.  It  is  obvious  that  the  density 
determination,  and  hence  the  molecular  weight  calculated  from 
it,  need  not  be  very  exact,  since  the  possible  molecular  weights 
which  correspond  to  a  given  empirical  formula  are  usually  quite 
far  apart;  in  the  case  taken  for  illustration,  they  would  be  30, 
60,  90,  etc.,  and  a  determination  which  was  within  five  units  of 
the  true  value  would  be  conclusive. 

The  molecular  weights  of  substances  which  cannot  be  vapor- 
ized without  decomposition  are  generally  found  from  the  effect 
which  a  given  weight  of  the  substance  has  in  lowering  the  freez- 
ing point,  or  in  raising  the  boiling  point  of  some  solvent.1 

Another  method  for  determining  molecular  weights  in  certain 
cases  depends  on  an  argument  which  may  be  made  from  the  com- 
position of  the  substance  as  compared  with  that  of  some  substi- 

1  For  these  methods  see  Ostwald-Luther's  Physico- Chemical  Measurements. 


12  INTRODUCTION    TO    ORGANIC   CHEMISTRY 

tution  product.  This  is  best  shown  by  an  example.  One  of  the 
compounds  whose  empirical  formulas  are  all  CH2O  is  an  acid. 
If  we  make  the  silver  salt  of  this  acid  and  determine  the  silver, 
we  find  that  it  amounts  to  64.64  per  cent,  of  the  salt;  the  rest 
of  the  salt — the  acid  radical — making  up  the  remaining  35.36  per 
cent.  Since  64.64  :  35.36  =  107.88  (atomic  weight  of  silver):  59, 
for  every  atomic  weight  of  silver  there  are  59  atomic  weight 
units  of  the  radical  which  contains  all  the  carbon  and  oxygen  of 
the  acid,  with  any  hydrogen  which  has  not  been  displaced  by  the 
silver  in  the  formation  of  the  salt.  Now  we  know  that  silver  has 
a  valence  of  one,  and  therefore  each  atomic  weight  of  silver  takes 
the  place  of  one  atomic  weight  of  hydrogen.  If  we  add  the  weight 
of  one  atom  of  hydrogen  to  the  atomic  weight  units  of  the  acid 
radical,  we  have  the  probable  molecular  weight  of  the  acid,  that  is, 
60.  The  simplest  formula  which  agrees  with  this  is  C2H4O2, 
that  of  the  silver  salt  being  C2H3AgO2.  But  here,  as  in  the  case 
of  the  empirical  formula,  any  multiple  of  this  would  satisfy  the 
facts  equally  well,  for  the  silver  salt  might  be  C4HeAg2O4,  or  any 
multiple  of  C2H3AgO2.  If  the  salt  which  we  analyzed  really 
had  one  of  these  formulas,  we  should  expect  that  an  acid  salt, 
containing  only  one  atom  of  silver,  could  be  obtained,  and  since 
we  find  in  this  case  that  such  a  salt  cannot  be  made,  the  simple 
formula,  C2H3AgO2,  is,  in  all  probability,  the  correct  one. 

Structural  Formulas. — In  organic  chemistry  we  not  only  find 
many  instances  of  different  compounds  which  have  the  same 
empirical  formulas,  and  which  must  be  distinguished  by  a  knowl- 
edge of  their  molecular  formulas,  but  there  are  also  frequent 
cases  in  which  two  or  more  compounds  have  the  same  molecular 
formulas  and  are  yet  very  different  substances.  There  is  only 
one  way  in  which  we  can  imagine  the  occasion  of  such  differences, 
and  that  is  by  different  relations  of  the  elements  to  each  other  in 
the  molecule.  These  we  represent  by  formulas  which  are  known 
as  constitutional,  structural,  or  graphic  formulas,  and  with  which 
the  student  is  familiar  to  some  extent  in  inorganic  chemistry, 


PRELIMINARY   DISCUSSION  13 

In  such  formulas,  the  atomic  symbols  are  connected  in  different 
ways  and  in  different  groups.  Compounds  of  the  same  mole- 
cular formula  but  of  different  properties  are  called  isomeric 
compounds  or  isomers,  and  the  phenomenon  is  known  as  isomer- 
ism.  The  subject  will  be  discussed  in  connection  with  the 
various  cases  of  isomerism  which  we  shall  meet  in  the  course  of 
our  study. 

Classification  of  Organic  Compounds. — For  reasons  that  need 
not  be  formally  discussed  at  this  point,  the  organic  compounds 
are  usually  treated  under  two  general  classes:  the  Aliphatic 
and  the  Aromatic  compounds.  These  names,  like  that  of  Organic 
Chemistry,  have  lost  much  of  their  original  significance — many  of 
the  aliphatic  compounds  have  no  direct  relationship  to  the  fats 
and  their  derivatives,  from  which  the  name  is  taken,  and  many  of 
the  aromatic  compounds  are  unlike  the  fragrant  substances  which 
suggested  their  name.  There  are,  however,  broad  lines  of  dis- 
tinction between  the  two  groups  of  compounds,  which  justify 
the  classification.  In  each  of  these  two  main  classes,  we  shall 
find  a  number  of  well-defined  smaller  groups  each  containing 
compounds  which  are  closely  related  to  each  other  in  both  their 
physical  and  chemical  properties,  such  as  the  several  groups  of  the 
hydrocarbons,  the  alcohols,  the  acids,  the  carbohydrates,  the 
phenols,  etc. 

Laboratory  Operations. — Many  of  the  reactions  for  the  prepara- 
tion of  organic  substances  proceed  very  slowly  as  compared  with 
those  familiar  in  inorganic  chemistry.  The  principal  reaction  is 
also  more  often  complicated  by  secondary  reactions,  and  therefore 
the  yield  of  the  desired  product  is  frequently  far  below  that 
indicated  by  the  equation  which  represents  the  reaction. 

Solvents  are  often  necessary  to  bring  about  the  intimate  contact 
which  is  necessary  for  the  reaction,  and  where,  as  is  generally  the 
case,  one  or  more  of  the  substances  is  insoluble  in  water,  various 
organic  solvents  are  employed,  such  as  alcohol,  acetone,  acetic 
acid,  chloroform,  ether,  benzene,  phenol,  etc.,  and  in  some 


14  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

instances,  sulphuric,  hydrochloric,  or  nitric  acid.  Frequently 
the  solvent  acts  also  as  a  necessary  diluent. 

The  temperatures  for  organic  reactions  are  usually  not  very  high. 
In  some  cases,  where  heating  is  necessary,  it  is  sufficient  to  distil 
the  mixture,  either  immediately  or  after  more  or  less  prolonged 
preliminary  boiling  with  a  reflux  condenser;  or  the  substances  may 
be  dissolved  in  a  high  boiling  solvent.  Higher  temperatures  than 
those  permitted  by  the  boiling  points  are  obtained  by  heating 
under  pressure,  ordinarily  in  sealed  glass  tubes. 

In  many  instances,  reactions  succeed  only  when  the  tem- 
perature is  kept  low,  on  account  of  the  instability  of  the  desired 
product  (as  in  the  preparation  of  the  diazo  compounds,  p.  313), 
or  because  other  products  are  formed  at  higher  temperatures. 
The  heat  developed  in  the  reactions  is  often  considerable,  and  its 
ill  effects  may  be  avoided  by  gradual  addition  of  the  reacting  sub- 
stances to  each  other  and  external  cooling  (cf.  pp.  159,  294), 
or  by  dilution  with  indifferent  solvents  such  as  water,  glacial 
acetic  acid,  alcohol,  ether,  or  benzene. 


CHAPTER  II 

THE  PARAFFINS  OR  HYDROCARBONS  OF  THE 
METHANE  SERIES 

Among  the  hundreds  of  compounds  which  contain  only  carbon 
and  hydrogen,  there  is  a  considerable  group  whose  members 
resemble  each  other  in  a  remarkable  manner.  Some  of  them  are 
gases,  some  are  liquids,  and  others  solids;  but  they  are  all  color- 
less, all  insoluble  in  water,  and  are  all  characterized  by  great 
chemical  indifference.  Even  such  powerful  agents  as  concen- 
trated sulphuric  acid,  chromic  acid,  and  fuming  nitric  acid,  fail 
to  attack  them  at  ordinary  temperatures.  At  higher  temperatures 
these  agents  act  very  slowly  with  the  production  of  carbon  dioxide 
and  water,  and  only  very  small  amounts  of  intermediate  com- 
pounds. Chlorine  is  the  only  agent  which  acts  on  these  substances 
at  all  readily  in  the  cold.  It  acts  more  rapidly  in  sunlight  or 
when  the  temperature  is  raised,  and  the  result  of  its  action  is  a 
step-by-step  replacement  of  hydrogen  by  chlorine.  This  may 
proceed  until  all  of  the  hydrogen  is  replaced  and  compounds  are 
formed  which  consist  of  carbon  and  chlorine  alone.  Bromine 
reacts  in  sunlight  with  the  liquid  and  gaseous  hydrocarbons  with 
the  production  of  similar  substituted  compounds. 

These  hydrocarbons  have  received  the  name  of  paraffins 
(parum  and  affinis)  on  account  of  their  chemical  indifference  or 
"little  affinity." 

The  results  of  analyses  and  molecular  weight  determinations 
show  that  their  formulas  can  be  arranged  in  a  regular  series.  The 

-    15 


1 6  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

hydrocarbon  of  the  lowest  molecular  weight,  16,  has  the  composi- 
tion Qj^JNj,  H  =  25,  and  these  data  lead  to  the  molecular  for- 
mula, CH4.  The  next  in  molecular  weight  contains  C  =  80,  H  =  20 
and  as  its  molecular  weight  is  30  its  formula  is  C2He.  The 
third  with  the  molecular  weight  of  44  has  C  =  8i.82,H  =  18.18, 
and  the  formula  C3H8.  These  molecular  weights  increase  from 
the  first  to  the  second,  and  from  the  second  to  the  third,  by  14 
atomic  weight  units,  and  the  formulas  by  an  increment  of  CH2. 
The  other  paraffins  have  molecular  weights  and  formulas  •which 
stand  in  a  like  relation  to  these  and  to  each  other,  so  that  the  mo- 
lecular weight  of  any  one  of  them  can  be  expressed  by  16  +  I4n, 
and  their  composition  by  CH4  +  nCH2,  where  n  is  any  number 
from  o  to  59.  The  last  expression  may  be  given  the  more  com- 
pact form,  CnH2n  +  2,  in  which  n  is  any  number  from  i  to  60. 
CnH2n  +  2  is,  therefore,  a  general  formula  for  the  paraffins.  Com- 
pounds having  such  relations  as  this,  which  can  be  expressed  by  a 
general  formula,  are  said  to  form  an  homologous  series.  The  per- 
centage of  hydrogen  decreases  rapidly  at  first,  and  then  more 
and  more  slowly  as  we  pass  from  CH4  to  the  higher  members  of 
the  series;  but  here,  again,  a  general  expression  may  be  formu- 
lated for  the  percentage  of  hydrogen  in  any  of  the  paraffins.  This 

£  ,     ,  ioo(n  +  i).i 

is :  per  cent,  of  hydrogen  =  - 

7n  +  i 

With  this  orderly  relationship  in  composition  and  molecular 
weight  there  is  also  found  a  generally  uniform  gradation  in  such 
physical  properties  as  the  boiling  and  the  melting  points.  Many 
of  the  series  from  n  =  i  to  n  =  60  are  known  and  have  been 
investigated,  and  the  others  could,  undoubtedly,  be  made  if  there 
was  any  special  object  in  so  doing.  Some  of  the  formulas  with 
the  names  and  the  melting  and  boiling  points  are  given  in  the 
following  table. 

1  In  this  discussion,  for  the  sake  of  greater  clearness,  the  atomic  weight  of 
hydrogen  has  been  taken  as  i  instead  of  1.008.  The  more  exact  formula  for 

the  percentage  of  hydrogen  is   I00-8  (n+I)_. 
7.oo8n  +  1.008 


PARAFFINS    OR   HYDROCARBONS    OF    METHANE   SERIES      17 


NORMAL  PARAFFINS 


Boiling  Point 

-160° 

-  93 

—  37 

0.6 

36.4 

70 

98.4 

125.6 

149-5 

173 

194 

214-5 
252.5 
287.5 

205  l 

2I51 

2341 

302! 

33I1 


But  the  number  of  hydrocarbons  in  the  group  is  very  much 
larger  than  indicated  by  this  list.  While  there  is  only  one  com- 
pound of  the  formula  CH4,  and  only  one  for  each  of  the  formulas 
CzH-e  and  C3Hs,  there  are  two  hydrocarbons  of  the  formula  C4Hio, 
three  whose  composition  and  molecular  weights  correspond  to 
CsH^,  and  a  rapidly  increasing  number  for  each  of  the  following 
members  of  the  series. 

As  was  stated  in  the  first  chapter,  the  explanation  of  such  "iso- 
meric"  compounds  is  found  in  the  theory  that  the  same  number 
of  atonis  is  differently  combined  in  molecules  of  the  same  com- 
position and  weight. 

In  the  theory  of  valency,  as  the  student  knows,  the  atoms  of  a 
compound  are  supposed  to  be  bound  together  by  the  force  of 

xAt  15  mm.  pressure. 
2 


Formula 

Name 

Melting  Point 

CH4 

Methane 

-184° 

C2H6 

Ethane 

-172 

C3H8 

Propane 



C4Hio 

Butane 

-135 

CsHi2 

Pentane 



CeHu 

Hexane 



C7H16 

Heptane 



CgHig 

Octane 



CgH^o 

Nonane 

-51 

CloH22 

Decane 

-31 

CnH24 

Undecane 

-26 

Ci2H26 

Dodecane 

—  12 

CuHso 

Tetradecane 

4 

CieH34 

Hexadecane 

18 

C2oH42 

Eicosane 

37 

C2lH44 

Heneicosane 

40 

C23H48 

Tricosane 

48 

CsiH64 

Hentriacontane 

68 

C35H72 

Pentatricontane 

75 

CeoHi22 

Hexacontane 

101 

1 8  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

chemical  affinity  acting  at  certain  points  or  through  certain  lines 
of  union  which  are  called  ''valencies."  The  number  of  valencies 
depends  on  the  nature  of  the  element,  and  is  determined  by  the 
study  of  the  simpler  compounds  which  it  forms  with  other  ele- 
ments— the  valence  of  hydrogen  being,  taken  as  the  unit.  Carbon 
is  tetravalent  in  such  simple  compounds  as  CH4,  CGU,  CO2;  and 
the  formulation  of  the  vast  majority  of  its  compounds  is  satis- 
factorily accomplished  by  the  use  of  the  tetrad  carbon  atom. 
(In  CO,  and  a  few  other  compounds  carbon  acts  as  a  dyad  and  in 
one  instance,  at  least,  carbon  appears  to  be  a  triad.)  Of  the  other 
"organic  elements,"  hydrogen  is,  of  course,  monovalent,  oxygen 
divalent,  and  nitrogen  either  trivalent  or  pentavalent. 

The  theory  of  valency  is  the  basis  on  which  organic  chemistry 
has  been  developed,  and  its  value  as  a  working  hypothesis  has 
been  abundantly  demonstrated  by  the  results,  which  prove  it  to 
have  been  one  of  the  most  fruitful  theories  of  natural  science.  By 
the  linking  of  atomic  symbols  in  accordance  with  the  valence 
theory  we  can  represent  in  graphic  or  structural  formulas  arrange- 
ments which  clearly  differentiate  and,  in  a  way,  explain  the 
various  organic  compounds. 

For  instance,  in  the  case  of  C4Hi0  two  different  arrangements 
can  be  made: 

H  H  H 

I  I  I 

H— C— H      CH3        H— C— H     H— C—H      CH3  CH3 

I  I  \/ 

H— C— EL      CH2  C— H  CH 

or  |       and  or 

H— C— H      CH2  H— C— H  CH3 

I  I  I 

H— C— H       CH3  H 


PARAFFINS    OR   HYDROCARBONS    OF   METHANE    SERIES       IQ 

and  for  C5Hi2,  the  three  arrangements: 

CH3  CH3      CH3  CHs 

I          \/  I 

CH2  CH  CH3— C— CH3 

I  I  I 

CH2  CH2  CH3 

I  I 

CH2  CH3 

CH3 

Moreover,  these  groupings  are  the  only  ones  which  can  be  made 
in  which  actual  differences  in  the  relations  of  the  atoms  are  indi- 
cated. Now  it  happens  that  there  are  only  two  different  com- 
pounds of  the  formula  C-iHio,  and  only  three  of  the  formula  CsHi2 
known,  in  spite  of  all  attempts  to  make  others;  and  this  agreement 
between  the  number  of  theoretical  formulas  and  the  facts  is  found 
to  extend  to  all  such  cases  of  chemical  isomerism — that  is,  in  no 
instance  is  a  larger  number  of  isomers  known  than  is  predicted  by 
the  possible  structural  formulas,  and,  though  in  many  cases  the 
whole  number  of  isomers  is  not  known,  the  validity  of  this  ex- 
planation has  been  abundantly  proved.  It  should  be  noticed, 
incidentally,  that  only  one  distinct  grouping  is  possible  for  the 
formulas  of  the  first  three  members  of  this  series. 

It  is  one  thing,  however,  to  find  that  for  the  observed  differences 
of  several  compounds  of  the  same  molecular  formula  there  is  an 
equal  number  of  possible  structural  formulas,  and  quite  another 
to  decide  which  particular  grouping  is  the  proper  representation 
of  each  of  these  compounds.  The  problem  can,  however,  be 
solved  by  studying  the  reactions  by  which  the  compounds  are 
synthesized  and  those  by  which  they  are  converted  into  other 
compounds.  Illustrations  of  the  methods  and  the  reasoning 
employed  for  the  selection  of  a  definite  arrangement  for  a  particu- 
lar compound  will  be  given  in  a  number  of  individual  instances. 

It  is  very  important  that  the  student  should  clearly  understand 


20  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

that  a  formula  of  any  sort  is  only  a  short-hand  or  pictorial  record 
of  observed  facts.  Hypothetical  structural  or  graphic  formulas 
are  often  useful  as  suggestions  and  incentives  for  investigation; 
but  no  formula  of  any  kind  should  be  accepted  unless  it  is  found 
to  be  in  accordance  with  all  the  experimental  facts.  It  may  not 
accurately  explain  all  these  facts,  and  indeed  few  if  any  of  our 
formulas  do;  but  it  must,  at  least,  not  be  in  contradiction  with 
any  of  them. 

The  empirical  formula  records  only  the  elementary  composition ; 
the  molecular  formula  adds  to  this  the  numbers  of  the  several 
atoms  in  the  molecule;  and  the  graphic,  constitutional,  or  struc- 
tural formula  is  an  attempt  to  represent  the  relations  of  these 
atoms  to  each  other. 

It  should,  perhaps,  be  pointed  out,  in  order  to  prevent  any 
possible  misunderstanding  later,  that  the  relative  positions  which 
are  given  the  symbols  in  the  usual  structural  formulas  are  entirely 
without  significance.  It  makes  no  difference  in  the  meaning  of 
the  formula  for  methane,  for  instance,  whether  we  write  CH4  or 

H  M 


H— C— H 


Of       <-CTT 
H  H 

In  all  three  cases  the  one  essential  fact  is  that  all  four  hydrogen 
atoms  are  directly  united  to  one  atom  of  carbon.  In  other  words, 
in  the  usual  formula  no  attempt  is  made  to  indicate  the  actual 
positions  or  space  relations  of  the  atoms  of  the  molecule. 

In  more  complex  formulas  the  position  of  the  symbols  is  fre- 
quently varied  for  the  purpose  of  bringing  out  some  special  point 
or  to  emphasize  certain  facts  in  the  behavior  of  the  compound; 
and  the  student  should  accustom  himself  to  recognize  the  iden- 
tity of  relationship  or  essential  "structure"  of  these  different 
arrangements. 


PARAFFINS   OR  HYDROCARBONS   OF   METHANE   SERIES       21 

We  shall  find,  however,  that  there  are  a  number  of  instances 
where  isomeric  compounds  show  differences,  usually  in  their 
physical  properties,  for  which  the  ordinary  method  of  formulation 
can  render  no  account;  and  that  here  a  satisfactory  explanation 
may  be  given  for  their  differences  by  formulas  which  indicate  the 
relative  positions  of  the  atoms  and  groups  in  space. 

It  is  obvious  that  empirical  and  simple  molecular  formulas  are 
of  little  use  in  organic  chemistry,  except  as  the  first  expression  of 
composition  and  the  basis  for  structural  formulas.  They  are  so 
similar  in  form  that  it  is  very  difficult  to  remember  them;  and  in 
many  instances,  as  has  been  said,  one  formula  often  applies  to  a 
number  of  substances  which  are  entirely  distinct  in  physical  and 
chemical  properties,  and  therefore  fails  to  represent  an  individual 
compound. 

On  the  other  hand,  the  structural  formula  is  of  the  greatest 
importance,  for  by  this  mode  of  representation  we  can  form  a 
clear  picture  of  the  differences  in  molecular  arrangement  which 
explain  the  differences  in  the  behavior  of  the  compounds.  In 
inorganic  chemistry  where  the  number  of  compounds  consisting 
of  the  same  two  or  three  elements  is  never  large,  such  formulas 
are  interesting,  but  by  no  means  so  necessary  for  our  study. 

A  good  exercise  for  the  student  at  this  point  is  to  write  all  of 
the  possible  formulas  for  a  few  of  the  paraffins  higher  than  CsH^. 
He  will  find  that  while  there  are  five  arrangements  for  CeHn, 
there  are  nine  for  C7Hi6  and  eighteen  for  C8H18.  Indeed,  the 
number  of  combinations  and  hence  of  the  possible  isomers  must, 
from  the  nature  of  the  case,  increase  very  rapidly.  There  are 
75  for  CioH22,  355  for  Ci2H26,  and  802  for  Ci3H28. 

The  paraffins  which  are  represented  by  formulas  in  which  the 
carbon  atoms  are  united  in  unbranched  chains,  that  is,  where  no 
carbon  atom  is  in  combination  with  more  than  two  other  carbon 
atoms,  are  termed  normal  paraffins.  It  is  these  which  are  given 
in  the  table  on  page  17.  The  isomers  or  iso-hydrocarbons  have 
branching  chains  of  carbon  atoms. 


22  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

Nomenclature. — The  first  four  of  the  normal  paraffins  have 
arbitrary  names;  the  higher  members  of  the  series  are  named 
numerically  by  the  use  of  the  Greek  numerals.  The  names  of 
all  paraffins,  normal  and  isomeric,  end  in  ane.  Since  ethane 
is  composed  of  two  CH3  groups,  CH3.CH3,  propane  of  a  CH3 
group  and  a  C2H6  group  (CH3.CH2),  butane  of  a  CH3  group  and  a 
CsHy  group  (CH3.CH2.CH2),  etc.,  and  as  these  groups  appear 
in  many  compounds,  it  is  convenient  to  have  simple  names  for 
them.  They  are,  therefore,  named  from  the  corresponding  hy- 
drocarbon containing  one  more  atom  of  hydrogen  by  substituting 
the  termination  yl  for  ane;  thus  CH3  is  methyl,  C2H5  is  ethyl, 
CzH.7  is  propyl,  etc.  Compounds  which  contain  these  groups 
are  very  commonly  named  from  the  groups,  so  that  the  names 
become  descriptive  of  the  composition.  Thus  ethane  is  di- 
methyl, propane  is  ethyl-methane,  butane  is  propyl-methane 
or  di-ethyl,  etc.  The  general  name  of  alkyl  is  given  to  these 
groups. 

The  iso-paraffins  are,  perhaps,  most  satisfactorily  named  on 
a  similar  principle,  as  substituted  methanes,  taking  the  carbon 
atom  which  is  united  to  the  largest  number  of  other  carbon 
atoms  as  the  carbon  of  the  original  methane.  Thus  the  two  iso- 
meric pentanes  whose  formulas  are  given  on  page  19  would  be 
called  dimethyl-ethyl-methane  and  tetramethyl-me thane;  iso- 
butane  would  be  trimethyl-methane.  The  formulas  of  these 
compounds  may  be  written  in  a  more  compact  manner  on  one 
line  with  points  to  separate  the  groups  and  indicate  the  valences 
instead  of  lines:  dimethyl-ethyl-methane  (CH3)2:CH.CH2.CH3 
or  (CH3)2:CH.C2H5,  tetramethyl-methane  (CH3)2:C:(CH3)2, 
trimethyl-methane  (CH3)3;CH. 

Occurrence  of  the  Paraffins. — Petroleum  consists  almost 
wholly  of  mixtures  of  hydrocarbons,  often  with  small  amounts 
of  compounds  containing  sulphur,  nitrogen,  and  occasionally 
phosphorus.  In  the  Pennsylvania  oils  the  hydrocarbons  are 
almost  exclusively  members  of  the  paraffin  series,  while  other 


PARAFFINS    OR  HYDROCARBONS    OF   METHANE   SERIES      23 

oils,  such  as  the  Russian,  are  chiefly  mixtures  of  other  hydro- 
carbons. From  the  Pennsylvania  petroleum  the  individual 
paraffins  from  CH4  to  C3oHe2  have  been  isolated.  The  process 
of  separating  the  single  hydrocarbons  from  such  mixtures  is, 
however,  a  difficult  and  tedious  matter,  so  that  petroleum  cannot 
be  regarded  as  a  practical  source  for  their  preparation. 

Crude  petroleum  finds  considerable  employment  as  fuel,  but 
much  of  it  is  separated  by  distillation  into  "fractions,"  which  are 
characterized  by  a  certain  range  of  the  boiling  point  and  have  a 
specific  gravity  lying  between  certain  limits.  Each  of  these 
fractions  contains  more  than  one  hydrocarbon,  and  in  the  order 
of  their  boiling  points  and  increasing  specific  gravities  are 
known  by  the  commercial  names  given  in  the  table: 

Boiling  Specific  Contains 

Between  Gravity  Chiefly 

Petroleum  ether  .....  4o°-6o°  0.665-0.670       CsH^-CeHu 

p      ..        f  Benzine  or  naphtha  ..   7o°-go°  0.680-0.720       C6H14-C7Hi8 

\  Ligroin  .............  Qo°-i2o°  ........... 

Kerosene  ...........  i5o°-3oo°  o.  780-0.820 

Lubricating  oils  ......  above  300° 

Paraffin  .......  melts  38°-56°  o  .  87-0  .  93 


These  products  are  purified  by  washing  successively  with 
sulphuric  acid  and  caustic  soda,  to  remove  basic  and  acid  im- 
purities. Sulphur  is  removed  by  treatment  with  copper  oxide. 
From  the  last  fraction,  solid  "paraffin"  is  separated  by  cooling. 

The  yield  of  the  more  valuable  light  oils  is  increased  by  carrying 
out  the  distillation  of  the  heavier  oils  in  such  a  way  that  part  of 
the  condensing  vapors  run  back  into  the  boiling  oil.  The  tem- 
perature is  so  high  that  the  condensed  hydrocarbons  are  decom- 
posed, or  "cracked,"  as  it  is  technically  termed,  into  others  of 
smaller  molecular  weight.  Distillation  under  pressure  is  also 
effective. 

Vaseline  or  petrolatum  is  obtained  from  the  residuum  of  the 
heavier  oils,  when  these  are  distilled  in  a  partial  vacuum. 

Since  all  inflammable  gases  and  vapors  form  explosive  mixtures 
when  mixed  in  certain  proportions  with  air,  the  lighter  and  more 


24  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

volatile  oils  must  always  be  used  with  great  care  to  avoid  the 
ignition  of  such  mixtures  by  a  flame  or  electric  spark.  The  occa- 
sional explosion  of  kerosene  lamps  is  due  to  the  presence  of 
some  of  these  lighter  oils,  which  should  have  been  removed 
in  its  preparation. 

The  quality  of  kerosene  is  tested  by  finding  at  what  tem- 
perature it  gives  vapors  which  "flash"  on  its  surface  when  it  is 
slowly  heated  and  a  small  flame  brushed  over  it  Jrom  degree  to 
degree.  This  " flashing  point"  should  be  above  the  temperature 
which  the  oil  in  a  lamp  can  reach.  A  "fire  test"  is  also  made, 
and  consists  in  determining  the  temperature  at  which  the  oil 
takes  fire  and  burns.  Both  the  flashing  point  and  the  fire  test 
depend  somewhat  on  the  apparatus  employed.  Each  of  the 
United  States  has  its  own  specification  and  method  of  testing  pre- 
scribed by  the  law. 

The  uses  of  the  various  petroleum  products  as  solvents,  for 
cleansing,  etc.,  as  fuels  and  illuminants,  as  in  gasoline  engines 
and  kerosene  lamps  and  stoves,  as  lubricating-  oils,  and,  in  the 
case  of  paraffine,  for  candles,  etc.,  are  well  known. 

While  petroleum  is  the  chief  natural  product  in  which  the 
paraffins  occur,  some  of  the  gaseous  members  of  the  series,  notably 
methane,  are  constituents  of  natural  gas,  and  of  the  "fire-damp" 
of  coal  mines;  and  some  of  the  solid  members  occur  in  earth  wax 
or  ozokerite.  Considerable  amounts  of  gasoline  are  obtained 
from  natural  gas.  Various  paraffins  are  products  of  the  natural 
decomposition  of  organic  matter,  or  are  produced  in  the  processes 
of  destructive  distillation  of  coal,  wood,  etc. ;  but  these  are  mostly 
the  first  members  of  the  series  or  those  of  large  molecular  weight 
which  form  the  solid  paraffins. 

Although  the  mixtures  of  the  various  hydrocarbons  of  the 
methane  series,  which  are  obtained  from  petroleum  and  other 
sources,  are  of  very  great  importance,  no  practical  application 
whatever  has  been  made  of  any  member  of  the  series  by  itself. 
The  individual  paraffins  are,  however,  of  great  interest  to  the 


PARAFFINS    OR   HYDROCARBONS    OF    METHANE    SERIES       25 

chemist,  not  only  in  themselves  and  in  the  relationship  they 
have  to  one  another,  but  also  because  many  other  organic  com- 
pounds may  advantageously  be  viewed  as  derived  from  them  by 
the  substitution  of  various  elements  or  groups  for  part  or  all  of 
the  hydrogen  they  contain,  and  can  be  made  in  the  laboratory 
in  this  way.  Since  the  same  remarks  apply  to  the  other  series 
of  hydrocarbons,  organic  chemistry  is  sometimes  denned  as  the 
"chemistry  of  the  hydrocarbons  and  their  derivatives" 

Methane,  CH4,  with  other  gaseous  paraffins,  escapes  from 
petroleum  as  it  issues  from  the  ground;  and  it  is  the  chief  compo- 
nent of  natural  gas  and  of  the  "fire-damp"  which  finds  its  way 
into  coal  mines  from  fissures  in  the  coal,'  and  often  occasions 
disastrous  explosions.  It  is  a  frequent  product  of  the  decomposi- 
tion of  organic  matter  under  certain  conditions,  as  when  vege- 
table matter — dead  leaves,  etc. — decays  under  water,  and  hence  is 
contained  in  the  gas  which  is  disengaged  on  stirring  the  bottom 
of  stagnant  pools.  On  this  account  it  has  sometimes  been  called 
"marsh  gas."  It  is  always  formed  in  the  destructive  distillation 
of  coal,  wood,  etc.;  and  is  present  in  coal  gas  to  the  amount  of 
30-40  per  cent. 

Methane  can  be  made  in  the  laboratory  by  several  methods, 
some  of  which  may  be  used  for  its  actual  preparation,  while 
others  are  chiefly  of  theoretical  interest.  We  shall  here,  and  in 
the  future,  designate  the  former  "methods  of  preparation," 
the  latter  "methods  of  formation." 

Formation. — (a)  Methane  is  produced  in  small  amounts,  but 
mixed  with  hydrogen  and  other  hydrocarbons,  when  an  electric 
arc  between  carbon  electrodes  is  formed  in  an  atmosphere  of 
hydrogen.  It  is  also  formed:  (b)  when  the  vapor  of  carbon  disul- 
phide  mixed  with  hydrogen  sulphide  or  with  steam  is  passed 
through  a  tube  containing  heated  copper.  The  reactions  are : 

CS2  +  2H2S  +  8Cu  =  4Cu2S  +  CH4 

CS2  +  2H2O  +  6Cu  =  2Cu2S  +  2CuO  +  CH4 


26  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

(c)  When  mixtures  of  carbon  monoxide  or  carbon  dioxide  and 
hydrogen  are  passed  over  finely  divided  nickel  (obtained  by  reduc- 
tion of  the  oxide  with  hydrogen)  which  is  heated  to  about  250°, 
the  nickel  acting  as  a  contact  agent.  If  the  gases  are  mixed  in 
the  proportion  indicated  by  the  equations,  the  reaction  is  complete 
and  the  methane  is  pure: 

CO  +  3H2  =  CH4  +  H2O 
C02-f  4H2 


When  aluminium  carbide  is  brought  into  water: 
A14C3  +  i2H2O  =  4A1(OH)3 


(e)  When  halogen  substitution  products  of  methane  are  re- 
duced by  "  nascent"  hydrogen. 

The  first  four  of  these  methods  show  that  methane,  and  there- 
fore the  great  variety  of  compounds  which  can  be  made  from 
it,  can  be  synthesized  from  the  elements;  for  carbon  disul- 
phide,  water,  both  of  the  oxides  of  carbon,  and  aluminium 
carbide  can  be  produced  by  the  direct  union  of  their  constituent 
elements. 

Preparation.  —  Some  of  the  methods  of  formation  can,  of  course, 
be  used  for  the  preparation  of  methane,  but  the  methods  chosen 
for  the  preparation  of  substances  are  naturally  selected  on  ac- 
count of  the  simplicity  of  the  apparatus  and  conduct  of  the  proc- 
ess, and  the  yield  of  the  resulting  product,  (i)  The  most 
usual  method  of  preparing  methane  is  by  heating  a  mixture  of 
sodium  acetate  and  soda-lime  (a  mixture  of  sodium  and  calcium 
hydroxides)/  Sodium  acetate  has  the  formula  C2H3NaO2,  and 
the  reaction  is: 

C2H3O2Na  +  NaOH  =  Na2CO3  +  CH4 

The  methane  made  in  this  way  is  not  quite  pure  and  cannot  be 
freed  from  small  amounts  (up  to  8  per  cent.)  of  hydrogen  which, 
with  other  substances,  is  formed  by  the  action  of  heat  on  sodium 


PARAFFINS   OR  HYDROCARBONS   OF   METHANE   SERIES       27 

acetate  alone.  (2)  Pure  methane  is  most  readily  prepared  from 
methyl  iodide,  CH3I  (made  from  methyl  alcohol),  by  placing 
in  an  alcoholic  solution  of  this  substance  some  zinc  which  has 
first  been  coated  with  copper  by  treatment  with  a  dilute  solution 
of  copper  sulphate.  A  compound  of  the  metal  with  the  methyl 
iodide  is  first  formed,  CH3ZnI,  and  then  this  reacts  with  the 
alcohol  or  the  water  which  is  mixed  with  it  as  follows: 

CH3ZnI  +  HOH  =  CH4  +  Znl(OH) 

Properties. — Methane  is  the  lightest  compound  gas  that  is 
known,  being  a  little  lighter  than  ammonia  and  having  the  spe- 
cific gravity  of  0.557  (a*r  =  I)-  Its  flame  is  almost  colorless,  and 
like  every  combustible  gas  and  vapor,  it  forms  explosive  mix- 
tures with  oxygen  or  with  air. 

In  common  with  the  other  paraffins,  methane  is  hardly  acted 
on  at  ordinary  temperatures  by  any  agent  except  chlorine  or 
bromine.  The  action  is  slow  in  diffused  daylight,  but  more  rapid 
in  sunlight.  The  chlorine  replaces  the  hydrogen  of  methane,  with 
the  production  of  hydrogen  chloride  and  the  successive  formation 
of  CH3C1,  CH2C12,  CHC13,  CC14.  When  mixed  with  twice  its 
volume  of  chlorine,  methane  explodes  in  direct  sunlight  with  the 
separation  of  finely  divided  carbon: 

CH4  +  2C12  =  4HC1  +  C 

By  reactions  with  methyl  chloride,  CH3C1,  the  synthesis  of 
organic  substances  can  be  carried  on  from  the  elements. 

As  it  has  proved  impossible  to  obtain  more  than  one  com- 
pound of  the  formula  CH3C1,  and  only  one  of  the  formula 
CH2Cl2,  the  four  hydrogen  atoms  of  methane  must  all  be 
similarly  related  to  the  carbon  atom. 

Ethane,  C2He,  occurs  in  petroleum  and  natural  gas.  It  may  be 
formed  (i)  by  the  reaction  of  sodium  or  zinc  on  methyl  iodide: 

2CH3I  +  2Na  =  2NaI  +  C2H6 


28  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

This  reaction  leads  to  the  conclusion  that  ethane  is  di-methyl 
with  the  constitutional  formula,  CH3.CH3.  Ethane  may  be  pre- 
pared, like  methane,  (2)  by  the  reduction  of  its  halogen  substi- 
tution products  by  the  action  of  coppered  zinc  on  an  alcoholic 
solution  of  ethyl  iodide,  C2H5I,  and  (3)  by  heating  the  sodium 
salt  of  propionic  acid,  C3H5O2Na,  with  soda-lime,  the  reaction 
being  like  that  for  the  preparation  of  methane  from  sodium  ace- 
tate. Ethane  is  similar  to  methane  in  its  properties,  but  is 
more  easily  liquefied  and  burns  with  a  slightly  luminous  flame. 

General  Methods  for  the  Formation  of  Paraffins. — i.  The 
first  method  just  given  for  the  production  of  ethane  (i)  may  be 
used  for  the  formation  of  the  other  hydrocarbons  of  this  series. 
When  two  different  alkyl  halides  are  employed,  however,  a  mix- 
ture of  products  results.  For  instance,  from  the  action  of  sodium 
on  a  mixture  of  methyl  and  ethyl  iodides  in  ethereal  solution, 
propane,  CH3.CH2.CH3,is  formed  by  the  union  of  the  methyl  and 
ethyl  radicals: 

CH3I  +  CH3.CH2I  +  2Na  =  CH3.CH2.CH3  +  2NaI 

but  at  the  same  time  ethane  is  formed  from  the  union  of  methyl 
to  methyl,  and  butane  from  the  union  of  two  ethyl  radicals. 
Since  the  mixed  products  are  not  easily  separated,  this  method  is 
chiefly  useful  in  syntheses  from  single  alkyl  halides,  which  yield 
hydrocarbons  containing  double  the  number  of  carbon  atoms  of 
the  halide. 
The  paraffins  may  also  be  formed: 

2.  From  halides  containing  the  same  number  of  carbon  atoms 
(a)  By  reduction  with  "nascent"  hydrogen  (sodium  amalgam, 
zinc  and  hydrochloric  acid,  or  concentrated  hydriodic  acid),     (b) 
By  the  formation  of  zinc  alkyls  and  their  reaction  with  water 
(p.  36).      (c)  By  means  of  the  Grignard  reaction  (p.  37).     The 
iodides  and  bromides  are  most  suitable  for  these  reactions. 

3.  By  distilling  the  sodium  salts  of  acetic  acid  or  its  homologues 
with  soda-lime.     The  product  is  a  hydrocarbon  whose  molecule 
contains  one  less  carbon  atom  than  the  salt: 


PARAFFINS    OR  HYDROCARBONS    OF   METHANE   SERIES       2Q 

CH3.CH2.CO.ONa  +  NaOH  =  CH3.CH3  +  Na2CO3 

4.  Another  reaction  by  which  two  like  alkyl  groups  may  be 
combined  to  a  paraffin  hydrocarbon  occurs  in  the  electrolysis  of 
the  organic  acids  or  salts  which  contain  these  groups.     By  the 
electrolysis  of  acetic  acid,  for  instance,  the  CH3  groups  which  it 
contains  unite  in  pairs  forming  ethane,  which  is  evolved  at  the 
positive   pole    together    with   carbon   dioxide,    while   hydrogen 
escapes  at  the  negative  pole: 

CH3.CO2H      CH3 

=  |        +  2C02  +  H2 
CH3.CO2H      CH3 

This  reaction  is,  however,  often  accompanied  by  other  reactions, 
giving  different  products  from  those  indicated  by  the  equation 
above. 

5.  By  the  addition  of  hydrogen  to  unsaturated  hydrocarbons: 

CH2:CH2  +  H2  =  CH3.CH3 

This  reaction  takes  place  readily  in  the  case  of  the  lower  members 
of  the  series  in  the  presence  of  platinum  black,  and  may  be  effected 
for  the  higher  members  by  heating  the  unsaturated  hydrocarbon 
with  hydriodic  acid  in  a  sealed  tube. 

The  possibility  of  isomeric  paraffins  begins  with  the  fourth, 
butane,  C4Hi0,  as  has  already  been  shown  (p.  18);  but  the  con- 
stitutional formula  for  propane,  CH3.CH2.CH3  with  a  CH2  and 
two  CH3  groups,  shows  that  two  different  mono-substitution 
products  are  possible,  CH3.CH2.CH2C1  and  CH3.CHC1.CH3; 
and  these  compounds  are  readily  prepared.  They  correspond 
to  the  two  butanes  which  may  be  regarded  as  propane  in  which 
one  hydrogen  atom  is  replaced  by  a  CH3  group. 

Very  few  of  the  iso-hydrocarbons  can  be  successfully  prepared 
by  the  sodium  synthesis,  because  of  the  mixture  of  products 
which  is  formed.  They  are  best  made  by  reduction  of  the  corre- 
sponding halides,  which  in  turn  are  prepared  from  the  correspond- 
ing alcohols  by  methods  which  will  be  discussed  further  on. 


30  INTRODUCTION   TO    ORGANIC    CHEMISTRY 

We  may  add  to  the  properties  of  the  paraffins,  that  as  the  molec- 
ular weights  increase  they  burn  with  a  more  luminous,  and  pres- 
ently with  a  smoky  flame,  and  that  the  higher  members  cannot 
be  distilled  at  ordinary  pressure,  but  undergo  decomposition  into 
other  lighter  hydrocarbons,  often  with  separation  of  carbon. 

The  iso-hydrocarbons  have  boiling  points  which  are  lower 
than  those  of  the  corresponding  normal  paraffins,  and  different 
from  each  other.  In  general,  a  higher  boiling  point  and  a  longer 
unbranched  chain  of  carbon  atoms  are  found  to  go  together. 
Thus  the  boiling  point  of  normal  pentane  with  a  chain  of  five 
carbon  atoms  is  36.4°,  that  of  dimethyl-ethyl-methane  (isopen- 
tane)  with  a  chain  of  four  atoms  is  30°,  and  that  of  tetra-methyl- 
methane,  9°. 

Identification  of  the  Paraffins. — An  organic  substance  which  is 
lighter  than  water  and  insoluble  in  it  but  soluble  in  ether  and 
benzene,  which  is  not  attacked  in  the  cold  by  fuming  nitric  acid 
or  concentrated  sulphuric  acid,  and  reacts  very  slowly  with  bro- 
mine, is  probably  a  paraffin.  Many  commercial  mixtures,  such 
as  the  products  of  petroleum,  when  subjected  to  these  tests  do 
show  some  reaction,  but  this  is  because  of  the  presence  of  small 
amounts  of  hydrocarbons  of  other  series,  and  after  the  partial 
reaction  is  over,  the  pure  paraffins  remain.  They  may  therefore 
be  purified  in  this  way.  The  individual  paraffins  are  identified 
by  their  melting  or  boiling  points,  and  by  the  results  of  quantita- 
tive analysis.  The  iso-compounds  are  distinguished  not  only 
by  melting  and  boiling-point  determinations  but  also  by  the 
substitution  products  which  can  be  obtained  from  them. 


CHAPTER  III 

THE  HALOGEN  SUBSTITUTION  PRODUCTS  OF  THE 
PARAFFINS 

The  chlorine  and  bromine  substitution  products  of  the  par- 
affins are,  as  already  indicated  (p.  15),  the  only  halogen  deriva- 
tives which  can  be  made  directly  from  the  hydrocarbons;  but  since 
this  action  gives  a  mixture  of  products,  it  is  not  a  very  practical 
method  for  their  preparation.  The  action  of  chlorine  and  bro- 
mine is  increased  by  heat  or  sunlight,  and  also  by  the  presence  of 
certain  substances,  such  as  ferric  chloride,  aluminium  or  antimony 
chloride,  or  iodine,  which  act  as  "halogen  carriers."  Alkyl  chlor- 
ides, bromides,  and  iodides  are  usually  prepared  from  the  corre- 
sponding alkyl  hydroxides  known  as  alcohols,  which  have  the 
general  formula,  CnH2n  +  iOH.  The  replacement  of  the  hy- 
droxyl  group  by  the  halogen  is  effected,  in  the  case  of  the 
lower  members  of  the  series,  by  the  action  of  the  gaseous 
hydrogen  halides  on  the  alcohol  in  the  presence  of  anhydrous  zinc 
chloride  which  acts  as  a  water-absorbing  agent.  For  instance: 

C2H5OH  +  HC1  ±5  C2H5C1  +  H2O 

Ethyl  Ethyl 

alcohol  chloride 

Zinc  chloride  cannot  be  employed  when  the  higher  alcohols 
of  the  series  are  used,  since  it  acts  directly  on  the  alcohol  and  gives 
rise  to  other  products. 

The  bromides  and  iodides  (but  not  the  chlorides)  can  be  pre- 
pared by  distilling  the  alcohols  with  an  excess  of  an  aqueous  solu- 
tion of  hydrobromic  or  hydriodic  acid.  In  some  instances  a  halide 


32  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

salt  is  mixed  with  the  alcohol  and  the  halogen  acid  set  free  by 
treatment  with  sulphuric  acid.  Ethyl  bromide,  C2H5Br,  for 
example,  is  readily  made  by  distilling  a  mixture  of  alcohol,  potas- 
sium bromide,  and  sulphuric  acid.  In  every  case  a  large  excess 
of  the  hydrogen  halide  is  necessary,  since  the  reaction,  as  indicated 
in  the  above  equation,  is  a  reversible  one. 

The  method  of  most  general  applicability  is  the  treatment  of 
the  alcohol  with  a  phosphorus  halide: 


3C3H7OH  +  PC13  =  3C3H7C1  +  P(OH)3 

Propyl  Propyl 

alcohol  chloride 

This  method  is  the  one  almost  always  used  in  the  preparation 
of  alkyl  bromides  and  iodides.  It  is  not  necessary,  however,  to 
employ  the  phosphorus  halides  themselves,  but  simply  to  add 
bromine  or  iodine,  a  little  at  a  time,  to  the  alcohol  in  which  red 
phosphorus  has  been  placed.  After  standing  for  some  time  the 
alkyl  halide  is  obtained  by  distillation. 

General  Properties. — Methyl  chloride,  methyl  bromide,  and 
ethyl  chloride,  are  gases  at  ordinary  temperatures.  The  other 
alkyl  halides  up  to  those  of  high  molecular  weight  are  liquids  which 
are  almost  insoluble  in  water,  but  very  soluble  in  alcohol  or  in 
ether.  The  lower  alkyl  halides  burn,  and  methyl  and  ethyl 
chlorides  give  a  green-edged  flame.  All  of  them  are  colorless, 
though  the  iodides  become  brown  after  a  time,  on  account  of 
iodine  which  is  separated  by  slight  spontaneous  decomposition 
and  dissolves  in  the  unchanged  iodide.  As  shown  in  the  follow- 
ing table  the  boiling  points  are  higher  as  the  molecular  weights 
increase;  and,  for  corresponding  halides,  are  highest  for  the 
iodides  and  lowest  for  the  chlorides.  The  specific  gravities  of  the 
compounds  of  a  given  halogen  decrease  as  the -molecular  weight 
is  larger,  and  the  specific  gravities  of  the  different  halides  of  the 
same  alkyl  show  the  same  gradation  as  the  boiling  points,  in- 
creasing from  the  chlorides  (which  are  all  lighter  than  water)  to 
the  iodides. 


HALOGEN   SUBSTITUTION  PRODUCTS    OF   PARAFFINS        33 

SOME  NORMAL  ALKYL  HALIDES   (Primary) 

CHLORIDE  BROMIDE                          IODIDE 

Boiling     Specific  Boiling         Specific      Boiling        Specific 

Point       Gravity  Point          Gravity        Point         Gravity 

Methyl —23.7°  0.952  (o°)  4-5°    i.73«  (o°)      45°     2.293  (18°) 

Ethyl 14       0.918  (8)  38.4     1.468  (13)      72.3    1.994  (14) 


Propyl    46.5  0.912(0)  71 

Butyl   78  0.907  (o)  101 

Amyl    107  0.901  (o)  129 

Hexyl 133  0.892  (16)  156 

Heptyl  159  0.881  (16)  179 

Octyl    180  0.880  (16)  199 


.383  (o)  102.5  1.786  (o) 

.305  (o)  130  1.643  (o) 

.246  (o)  156  1.543  (o) 

.193  (o)  182  1.461  (o) 

.113  (16)  201  1.386  (16) 

.116  (16)  221  1.345   (16) 


The  relation  between  structure  and  physical  properties  is 
illustrated  by  the  following  table  of  the  boiling  points  and  specific 
gravities  of  the  isomeric  butyl  halides: 

CHLORIDE  BROMIDE  IODIDE 

Boiling      Specific        Boiling        Specific        Boiling  Specific 
Point       Gravity         Point         Gravity         Point    Gravity 

Normal  butyl 78°      0.907(0°)      101°     1.305(0°)      130°  1.643  (o°) 

CH3.CH2.CH2.CH2X 

Iso-butyl 68.5    0.895(0)       92        1.204X16)     119    1.640(0) 

(CH3)2CH.CH2X 

Secondary  butyl 67.5     0.871(20)     91.3     1.250(25)     119    1.626(0) 

CH3.CH2.CHX.CH3 

Tertiary  butyl 55        0.866(0)       72        1.215(20)     100    1.571(0) 

(CH8)2CX.CH3 

The  chemical  reactivity  of  the  normal  halides  is  greatest  in  the 
iodides  and  least  in  the  corresponding  chlorides;  it  also  increases 
from  the  higher  members  to  the  lowest.  Methyl  iodide  is,  there- 
fore, the  alkyl  halide  of  greatest  activity.  Alkyl  iodides  are 
converted  into  bromides  or  chlorides  by  bromine  or  chlorine. 
Bromine  is  not  displaced  by  chlorine,  but  a  bromide  may  be 
changed  into  a  chloride  by  antimony  pentachloride.  The 
halides  react  more  or  less  readily  with  many  substances,  and  are 
consequently  of  great  importance  in  organic  synthesis. 

The  following  are  typical  reactions: 

i.  With  Hydroxyl  Compounds. — With  water  or  alkalies  the 
3 


34  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

halogen  is  exchanged  for  the  hydroxyl  group  and  alcohols  are 
formed: 

CH3I  +  HOH  <=»  CH3OH  +  HI 

Methyl  Methyl 

iodide  alcohol 

C2H5Br  +  KOH  =  C2H5OH  +  KBr 

Ethyl  Ethyl 

bromide  alcohol 

The  reaction  with  water  is  reversible,  and  to  render  it  complete, 
heat  and  a  considerable  excess  of  water  are  necessary,  while  that 
with  the  base  goes  more  readily.  Moist  silver  oxide,  which 
reacts  like  a  hydroxide,  effects  the  exchange  still  more  easily, 
and  usually  without  heating: 

C2H5C1  +  AgOH  =  C2HBOH  +  AgCl 

Ethyl  Ethyl 

chloride  alcohol 

This  replacement  of  the  halogens  by  hydroxyl  takes  place 
most  easily  with  the  alkyl  iodides  and  least  rapidly  with  the 
chlorides.  If,  however,  potassium  hydroxide  acts  in  an  alcoholic 
instead  of  an  aqueous  solution,  the  character  of  the  reaction  is 
altered:  the  replacement  by  hydroxyl  does  not  occur,  but  instead, 
the  halogen  and  an  atom  of  hydrogen  are  withdrawn  from  the 
halide  with  the  production  of  an  "  unsaturated "  hydrocarbon 
(p.  42): 

CH3.CH2Br  +  KOH  =  CH2:CH2  +  KBr  +  H2O 

Ethyl  bromide  Ethylene 

2.  With  Certain  Salts. — The  inorganic  salts  most  employed  in 
the  reactions  are  those  of  silver.  With  these  a  fairly  ready  reac- 
tion usually  takes  place,  with  the  formation  of  the  insoluble 
silver  halide  and  compounds  in  which  the  alkyl  group  is  united 
to  the  acid  radical  of  the  silver  salt,  thus: 

CH3I  +  AgN03  =  CH3NO3  +  Agl 

Methyl  Methyl 

iodide  nitrate 

2C2H5Br  +  Ag2S04  =  (C2H5)2SO4  +  2AgBr 

Ethyl  Ethyl 

bromide  sulphate 


HALOGEN   SUBSTITUTION   PRODUCTS   OF   PARAFFINS        35 

Organic  salts  of  sodium  and  potassium  act  in  a  similar  way, 
CH3C1  +  KCN  =  CH3CN  +  KC1 

Methyl  Methyl 

chloride  cyanide 

C2H5I  +  C2H3O2Na  =  C2H3O2C2H5  +  Nal 

Ethyl  Sodium  Ethyl 

iodide  acetate  acetate 

The  alkyl  compounds  formed  in  these  reactions  are  named  as 
alkyl  salts  of  the  several  acids,  and  are  given  the  group  name  of 
"esters"  or  "ethereal"  salts.  The  alkyl  halides  themselves 
obviously  belong  to  this  same  group. 

3.  With  ammonia,  the  halogen  is  replaced  by  NH2,  the  "  amino" 
group, 

C2H5Br  +  NH3  =  C2H5NH2.HBr 

Ethyl  Ethyl  amine 

bromide  hydrobromide 

4.  The  alkyl  halides,  as  well  as  all  halogen  substitution  products 
of  the  paraffins,  are  converted  into  the  respective  hydrocarbons 
by  "nascent"  hydrogen: 

C2H6I  +  HH  =  C2H6  +  HI 

Attention  should  be  called  to  the  fact  that  the  metathetical 
reactions  with  alkyl  halides,  which  have  been  described,  progress 
slowly  as  compared  with  the  almost  instantaneous  reactions  of 
this  kind  which  occur  between  inorganic  salts  and  ba,ses.  The 
explanation  given  for  this  is  that  the  organic  halides  are  iC*iized 
very  slightly,  if  at  all. 

5.  With  Metals. — The  reaction  of  alkyl  halides  with  sodium  has 
already  been  given  (p.  28)  as  a  means  of  synthesizing  the  paraffins. 
A  compound  containing  zinc  was  also  used  for  the  same  purpose. 
Zinc,  magnesium,  and  some  other  metals  react  with  the  alkyl 
halides  as  follows: 

C2H6I  +  Zn  =  C2H6ZnI 

When  this  zinc  ethyl  iodide  is  boiled  for  some  time  it  is  converted 
into  zinc  ethyl  (C2H5)2Zn: 

2C2H5ZnI  =-  (C2HB)2Zn  -f  ZnI2 


36  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

Zinc  ethyl  iodide  is  a  solid,  but  the  zinc  alkyls  are  liquids  of 
repugnant  odor,  which  take  fire  spontaneously  in  the  air,  so  that 
their  preparation  and  their  use  as  reagents  must  all  be  conducted 
in  an  atmosphere  of  an  indifferent  gas,  usually  carbon  dioxide. 
They  are  immediately  decomposed  by  water  with  the  produc- 
tion of  hydrocarbons: 

(C2H5)2Zn  +  2H20  =  2C2H6  +  Zn(OH)2 

The  Grignard  Synthesis. — The  use  of  zinc  alkyls  and  their 
halide  salts  has  been  generally  displaced  by  the  employment  of 
corresponding  magnesium  compounds;  since  it  has  been  found  that 
these  are  more  easily  prepared,  and  have  the  further  advantage 
of  not  igniting  spontaneously  in  the  air. 

•  Clean  dry  magnesium  turnings  are  covered  with  anhydrous 
ether  and  the  organic  halogen  compound  is  gradually  added. 
Absence  of  moisture  is  essential  to  success.  After  the  reaction, 
evaporation  of  the  ether  leaves  the  magnesium  compound  in 
combination  with  one  molecule  of  ether,  e.g.,  C2H5MgI,  (C2Hs)2O. 
Other  solvents  besides  ether,  such  as  benzene,  can  be  used,  if  a 
little  ether  or  anisol  is  added  as  a  catalyzer,  and  in  this  case  the 
magnesium  compound  is  obtained  free  from  ether.  In  many 
instances  the  preliminary  preparation  of  the  magnesium  com- 
pound is  not  necessary,  the  two  organic  substances  which  are 
to  be  synthesized  being  brought  together  in  the  presence  of  mag- 
nesium and  ether. 

Almost  all  the  halogen  derivatives  of  organic  compounds,  ex- 
cept acyl  halides  (p.  114),  form  addition  compounds  .with  magne- 
sium, and  these  substances,  which  are  called  Grignard  reagents, 
are  of  the  greatest  service  to  the  organic  chemist  on  account  of 
the  wide  variety  of  syntheses  which  can  be  effected  by  their 
means.  Some  of  the  reactions  with  Grignard  reagents  are 
given  here  for  convenience  in  future  reference. 

i.  With  water  and  other  hydroxyl  compounds,  they  yield 
hydrocarbons: 

CH3MgBr  +  H2O  =  CH4  +  MgBrOH 
C6H5MgBr  +  H20  =  C6H6  +  MgBrOH 


HALOGEN   SUBSTITUTION  PRODUCTS    OF   PARAFFINS        37 

2.  They  absorb  carbon  dioxide,  forming  products  which  yield 
organic  acids  when  treated  with  inorganic  acids: 

C2H6MgI  +  CO2  =  C2H5CO.OMgI 
C2H5CO.OMgI  +  HC1  =  C2H5CO.OH  +  MglCl 

3.  They  absorb  dry  oxygen  and  the  products  yield  primary 
alcohols  or  phenols  when  treated  with  an  acid: 

2RMgBr  +  O2  =  2RO.MgBr 
RO.MgBr  +  HC1  =  R.OH  +  MgBrCl 

4.  They  form  additive  compounds  with  most  substances  which 
contain  a  carbonyl  group  (CO),  and  these  yield  alcohols  when 
acted  on  by  water  or  an  inorganic  acid.     In  this  way  primary 
alcohols  may  be  prepared  by  means  of  formaldehyde: 


C2H5MgI  +  HCHO  =  C2K&^X 

X)MgI 

C2H6C^  +  HC1  =  C2H5CH2OH  +  MglCl 

\)MgI 

With  other  aldehydes  secondary  alcohols  are  formed: 


H  /H 

Mgl 


CH3MgI  =  (CH3)2C< 

X)] 


Aldehyde 

/H 

(CH3)2C<;  +  HC]  =  (CHC)2  CH.OH  +  MglCl 

X)MgI 

Ketones,  e.g.,  CH3.CO.CH3,  and  esters,  in  a  similar  manner  give 
tertiary  alcohols. 

5.  Aldehydes  can  be  prepared  from  formic  esters,  and  ketones 
from  cyanogen,  cyanides,  and  amides. 

6.  With  many  halides  of  metals  and  non-metals   they  enter 
into  reaction  with  the  production  of  the  alkyl,  or  alkyl-halogen 
derivatives  of  these  elements: 


38  INTRODUCTION    TO    ORGANIC    CHEMISTRY 


SnBr4  +  4C2H5MgBr  =  ( 
SiCl4  +  C2H5MgBr  =  C2H5SiCl3  +  MgBrCl 

Methyl  chloride  is  a  commercial  product  made  from  trimethyl- 
amine  hydrochloride  (p.  132),  which  is  obtained  as  a  by-product 
in  the  beet-sugar  industry.  It  is  compressed  to  a  liquid  and 
used  for  the  production  of  cold  (like  ammonia),  and  is  extensively 
employed  in  the  manufacture  of  various  coal  tar  dyes.  Ethyl 
chloride  is  also  made  on  the  large  scale  and  used  in  the  prepara- 
tion of  ethyl  mercaptan,  C2H5SH  (p.  238)  which  is  employed  in 
making  "sulphonal"  (p.  240). 

While  there  is  only  one  methyl  and  one  ethyl  chloride,  bromide, 
or  iodide  known  or  possible,  isomeric  alkyl  halides  begin  with 
the  two  propyl  halides,  CH3CH2CH2C1,  CH3.CHC1.CH3,  and  in- 
crease rapidly  in  number  as  we  go  higher  in  the  series.  There 
are  four  butyl  bromides,  CH3.CH2.CH2.CH2Br,  (CH3)2CH.- 
CH2Br,  CH3.CH2.CHBr.CH3,  and  (CH3)3CBr;  and  eight 
pentyl  bromides. 

Among  the  halogen  substitution  products  of  the  paraffins, 
which  contain  more  than  one  halogen  atom,  may  be  mentioned: 
Methylene  iodide,  CH2I2,  which  is  one  of  the  heaviest  known 
liquid  compounds  (specific  gravity  3.292  at  1  8°).  By  mixing  with 
benzene,  liquids  of  any  specific  gravity  between  0.8736  (benzene) 
and  3.292  can  be  prepared,  and  may  be  used  for  the  indirect  spe- 
cific gravity  determination  of  solids,  and  for  the  separations  of 
solids  of  different  specific  gravities.  It  is  made  by  the  reduction 
of  iodoform,  or  tri-iodomethane,  by  hydriodic  acid  in  the  presence 
of  phosphorus: 

CHI3  +  HI  =  CH2I2  +  Is 

This  is  a  typical  instance  of  the  use  of  hydriodic  acid  as  a  reduc- 
ing agent.  The  student  will  recall  from  his  study  of  inorganic 
chemistry  that  hydrogen  iodide  is  an  endothermic  and  hence  an 
unstable  compound,  separating  easily  into  hydrogen  and  iodine. 
The  phosphorus  facilitates  the  reaction  by  uniting  with  the  iodine 


HALOGEN   SUBSTITUTION   PRODUCTS    OF   PARAFFINS        39 

as  it  is  set  free;  the  phosphorus  iodide  then  reacts  with  the  water 
which  is  present,  giving  phosphorous  acid  and  hydriodic  acid 
again. 

Tri-iodomethane,  CHI3,  commonly  known  as  iodoform,  is  a 
yellow  crystalline  substance,  which  is  prepared  by  warming  an 
aqueous  solution  of  alcohol  and  sodium  carbonate  with  iodine. 
Its  formation  is  often  used  as  a  test  for  alcohol,  but  several  other 
organic  substances  give  iodoform  under  similar  conditions.  It 
is  used  as  an  antiseptic  in  surgery,  often  in  preparations  where 
it  is  mixed  with  other  substances  to  disguise  its  peculiar  odor. 

Tri-chlormethane,  CHC13,  or  chloroform,  is  the  well-known 
anaesthetic  which  was  discovered  in  1831  and  first  used  for  this 
purpose  in  1848.  It  is  prepared  by  the  action  of  bleaching  powder 
on  alcohol  or  acetone  or  from  chloral  hydrate  by  reactions  which 
will  be  discussed  under  those  topics.  Chloroform  is  a  colorless 
liquid  of  ethereal  odor  and  a  sweetish  taste.  It  is  slightly  soluble 
in  water  to  which  it  imparts  its  odor  and  taste.  It  is  readily 
volatile,  but  not  inflammable.  Chloroform  is  an  excellent  solvent 
for  many  organic  compounds;  it  dissolves  rubber  and  fats,  and  is 
a  useful  cleansing  agent.  In  the  air  and  light  chloroform  under- 
goes a  slow  decomposition  with  the  formation  of  chlorine,  hydro- 
gen chloride,  and  carbonyl  chloride,  COCU.  Consequently  great 
care  must  be  taken  in  regard  to  its  purity  when  it  is  used  for 
anesthesia.  When  heated  with  an  alcoholic  solution  of  potas- 
sium hydroxide,  chloroform  is  decomposed  with  the  formation  of 
potassium  formate: 

CHC13  +  4KOH  =  HCO.OK  +  3KC1  +  2H2O 

Chloro-  Potassium 

form  formate 

If  ammonia  is  added  to  the  mixture  of  alcoholic  potash  and 
chloroform,  potassium  cyanide  is  produced: 

CHC13  +  NH3  +  4KOH  =  KCN  +  3KC1  +  4H2O 


INTRODUCTION   TO   ORGANIC   CHEMISTRY 


A  similar  reaction  occurs  when  a  primary  amine  (p.  127)  is 
used  in  place  of  ammonia,  and  the  unmistakable  odor  of  the  prod- 
uct serves  as  a  test  for  chloroform  and  for  the  primary  amines 
(cf.  p.  132). 

Tetra-chlormethane,  CCU,  or  carbon  tetrachloride,  is  the  final 
product  when  chlorine  acts  on  methane.  It  is  prepared  commer- 
cially by  passing  the  vapor  of  carbon  disulphide  mixed  with  chlo- 
rine through  red-hot  porcelain  tubes,  or  by  leading  chlorine  into 
the  liquid  disulphide  in  which  a  little  iodine  has  been  dissolved, 
and  which  acts  as  a  catalyzer: 


CS2 


=  CC14  +  S2C12 


Carbon  tetrachloride  is  a  heavy  liquid  which  is  not  inflammable 
and  is  an  excellent  solvent  for  fats.  It  is  sold  for  extinguishing 
fire  as  "pyrene,"  and  is  much  used  for  cleansing  purposes,  often 
mixed  with  benzine  or  gasoline,  under  the  name  of  "carbona." 

It  is  hydrolyzed  by  a  hot  solution  of  potassium  hydroxide  with 
the  production  of  potassium  carbonate: 

CC14  +  6KOH  =  K2CO3  +  4KC1  +  3H2O 

On  heating  with  "molecular"  silver,  tetrachlor-methane  is  con- 
verted into  hexachlorethane,  CCls.CCls,  a  crystalline  substance  of 
camphor-like  odor,  which  is  hydrolyzed  by  potash  at  200°  into 
potassium  oxalate. 

SOME  POLYHALOGEN  DERIVATIVES 


CHLORIDE — 

Boiling    Specific 
j  Point     Gravity 

Methylene,  CH2X24i.6°      1.38 
Methenyl,  CHX3    61  1.50 

Carbon  tetrahalide, 


. BROMIDE • -IODIDE • — 

Boiling    Specific      Boiling  Specific 

Point     Gravity        Point  Gravity 

1 80° 


CX4 
Ethylene, 

CHaXCHaX 
Ethylidene, 

CH3.CHX2 


76.8        1.63 


83.7 


57-5 


1.27 


98-5° 

i89 

129 

112.5 


2.50 
2.90 


2.18 


3-33 
melts  119°    4.01 

unstable 

2.07 

178  2.84 


HALOGEN   SUBSTITUTION   PRODUCTS    OF   PARAFFINS        41 

While  the  chlorine  substitution  products  of  the  paraffins,  which 
contain  two  or  more  chlorine  atoms,  can  be  formed  by  direct 
step-by-step  replacement  of  hydrogen  with  chlorine,  this  method 
is  not  a  practical  one  for  the  preparation  of  the  individual  members, 
because  of  the  mixtures  it  gives.  Hence  other  methods  are  em- 
ployed for  making  the  chlorides  and  other  polyhalogen  derivatives. 

Besides  such  special  methods  as  have  just  been  given  for  the 
methane  derivatives,  there  are  certain  methods  of  general  ap- 
plication for  the  derivatives  of  the  higher  paraffins.  Dihalogen 
compounds,  in  which  the  two  halogen  atoms  are  united  to  one 
carbon  atom,  are  obtained  by  the  action  of  phosphorus  pentahal- 
ides  on  aldehydes  and  ketones: 

CH3.CHO  +  PC15  =  CH3.CHC12  +  POC13 

Aldehyde  Ethylidene 

chloride 

CH3.CO.CH3  +  PC15  =  CH3.CC12.CH3  +  POC13 

Acetone  Dichlorpropane  (2.2) 

The  isomeric  dihalogen  derivatives  with  the  halogen  atoms 
united  to  different  carbon  atoms  can  be  made  from  the  correspond- 
ing dihydroxyl  alcohols — glycols — as  the  monohalogen  com- 
pounds are  from  the  simple  alcohols — the  reaction  involving  two 
steps: 

CH2OH.CH2OH  ->  CH2Br.CH2OH  ->  CH2Br.CH2Br 

Glycol  Glycolbromhydrin  Ethylene  bromide 

These  halides  are  also  the  product  of  the  direct  addition  of 
halogen  to  unsaturated  hydrocarbons  of  the  olefine  series  (p.  44) : 

CH2:CH2  +  Br2  =  CH2Br.CH2Br 

Ethylene  Ethylene  bromide 

Compounds  of  this  type  are  useful  in  synthetic  work,  since 
they  may  form  a  step  in  the  conversion  of  a  monosubstituted 
compound  to  various  disubstituted  compounds.  We  shall  meet 
with  illustrations  of  such  transformations. 

It  should  be  remarked  that  isomerism  in  the  alkyl  polyhalides 
begins  with  the  derivatives  of  ethane.  Thus  there  are  two  di- 


4ia  INTRODUCTION    TO  ORGANIC  CHEMISTRY 

halides  of  ethane  represented  by  the  formulas,  CH2C1.CH2C1,  eth- 
ylene  chloride,  and  CH3.CHC12,  ethylidene  chloride.  Similarly 
there  are  two  tri-halides,  two  tetra-halides,  but  only  one  penta- 
and  one  hexa-halide.  As  we  go  higher  in  the  series  the  number  of 
halogen  substituted  isomers  increases  rapidly. 

Hydrolysis  of  Halogen  Derivatives. — All  the  halogen  deriva- 
tives of  the  paraffins  are  subject  to  hydrolysis.  The  normal 
course  of  the  hydrolysis  is  the  replacement  of  each  halogen  atom 
by  an  hydroxyl  group  (cf.  p.  34).  When  the  compound  contains 
only  one  halogen  atom  attached  to  any  one  carbon  atom,  the 
product  is  the  corresponding  hydroxyl  compound — a  simple  or  a 
polyhydroxyl  alcohol  (p.  59).  But  when  the  halogen  derivative 
contains  groups  of  the  types:  —  CHX2,  —  CX2— ,  or  —  CX3, 
which  would  give  two  or  three  hydroxyl  groups  united  to  the  same 
carbon  atom,  such  products  being  unstable  pass  at  once  into 
stable  forms  by  splitting  off  water.  Thus  from  R.CHX2  we  get 
an  aldehyde,  R.CHO  (p.  77);  from  R.CX2.R,  a  ketone,  R.CO.R 
(p.  89);  and  from  R.CX3,  an  acid,  R.CO.OH  (pp.  98,  99,  103). 


CHAPTER  IV 
UNSATURATED  HYDROCARBONS 

There  are  two  other  series  of  hydrocarbons,  which  are  so  re- 
lated to  the  paraffins  and  to  each  other  that  a  brief  considera- 
tion of  them  may  properly  be  given  at  this  point.  In  each  of  these 
series  the  members  show  a  constant  difference  of  14  between  their 
molecular  weights  and  consequently,  like  the  paraffins,  a  formula 
difference  of  CH2.  The  percentage  of  hydrogen  is,  however,  less 
than  in  the  corresponding  paraffins  which  have  the  same  number 
of  carbon  atoms,  and  less  in  one  series  than  in  the  other;  the 
difference  expressed  in  their  formulas  being  that  of  two  atoms  of 
hydrogen  in  each  case.  The  general  formulas  for  these  series 
are,  therefore,  CnH2n  and  CnH2n  _  2.  In  neither  of  these  series  is 
a  compound  known  which  contains  only  one  carbon  atom.  Such 
compounds  would  have  the  formulas,  CH2  and  CH,  with  carbon 
acting  as  a  divalent  element  in  one,  and  as  a  monovalent 
element  in  the  other.  Both  series  begin  with  compounds  con- 
taining two  atoms  of  carbon:  C2H4,  ethylene,  and  C2H2,  acetylene; 
and  the  series  are  called  from  these  first  members  the  ethylene 
series  and  the  acetylene  series,  respectively.  It  is  characteristic 
of  the  hydrocarbons  of  both  series  that  they  absorb  chlorine  and 
bromine,  uniting  additively  with  these  halogens  to  form  compounds 
of  the  types,  CnH2nCl2  and  CnH2n_2Cl4,  substances  which  can  be 
formed  from  the  corresponding  paraffins  by  substitution,  and  which 
can  be  converted  into  these  paraffins  by  nascent  hydrogen. 

On  account  of  this  behavior,  the  hydrocarbons  of  these  series 
are  termed  " unsaturated"  hydrocarbons.  In  making  a  graphic 
formula  for  ethylene,  with  the  assumption  that  carbon  is  here,  as 

42 


43  UNSATURATED  HYDROCARBONS 

H-C-H 

usually,  tetravalent,  we  must  write          II        ,  with  a  double  bond 

H-C-H 

between  the  carbon  atoms.  Any  other  formula  would  require 
an  unusual  valency  for  carbon.  With  a  very  few  exceptions,  such 
as  CO,  carbon  appears  everywhere  to  be  tetravalent,  and  there 
seems  to  be  no  good  reason  for  believing  that  its  valency  in  these 
compounds  is  an  exception  to  the  general  rule.  On  the  contrary, 
the  facts  that  a  hydrocarbon  of  the  formula  CH2  cannot  be  ob- 
tained, and  that  only  one  compound  of  the  type  CH2.CHC1 
can  be  made,  are  in  favor  of  the  tetravalency  of  carbon  in  ethylene 
and  the  symmetrical  formula,  CH2:CH2.  Again,  if  carbon  was 
here  trivalent,  we  might  expect  to  find  hydrocarbons  containing  a 
single  trivalent  atom,  such  as  C=H3.C  =  H2,  which  must  then  of 
necessity  have  an  odd  number  of  hydrogen  atoms.  But  no  such 
compounds  are  known,  and  on  the  contrary,  all  formulas  oj 
known  hydrocarbons  contain  an  even  number  oj  hydrogen  atoms. 

CH2 
The  symmetrical  formula  II        with  the  double  bond  is,  there- 

CH2 

fore,  usually  accepted  for  ethylene  and  similar  formulas  for  its 
homologues;  but  it  must  be  remarked  that  the  double  bond, 
instead  of  denoting  a  firmer  union,  indicates  a  weak  point  in 
the  molecule.  It  readily  gives  place  to  a  single  linkage,  as  in 
the  reaction  with  bromine: 

C  =  H2     *  CH2Br 

II  +  Br2  =   | 

C  =  H2  CH2Br 

and  in  oxidation  processes  is  the  point  where  the  compound  breaks 
down  most  easily  with  the  production  of  substances  which  have 
a  smaller  number  of  carbon  atoms  in  the  molecule. 
The  members  of  the  ethylene  series  have  only  one  double  bond, 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  44 

as    for    instance,    propylene  CH3.CH:CH2,  and    the   isomeric 
butylenes, 


av 

CH3.CH2.CH:CH2,    CH3.CH:CH.CH3,  and  >C:CH2. 

CH/ 

In  acetylene,  C2H2,  a  triple  bond  between  the  two  carbon  atoms 
is  indicated  for  reasons  of  the  same  kind  as  those  given  for  the 
double  bond  in  the  ethylene  series,  and  this  triple  bond  is  weaker 

C—  H 
than  the  double  bond.     Acetylene  is  III         ;  allylene,  or  methyl- 

C—  H 
acetylene,  the  next  number  of  the  series,  is  CH3.C  !  CH. 

The  acetylene  series  contains  two  groups  —  the  acetylene  group 
proper,  in  which  there  is  one  triple  bond;  and  the  di-olefines, 
which  are  isomeric  with  the  acetylenes,  but  have  two  double 
bonds  instead  of  one  triple  bond.  Thus,  allene,  CH2iC:CH2, 
a  di-olefine,  is  isomeric  with  allylene  given  above. 

The  name  olefine  (oil-forming)  was  given  to  ethylene  because 
this  gas  forms  an  oil  by  its  additive  reaction  with  chlorine. 
From  this  the  general  name  of  olefines  was  given  to  the  members 
of  the  ethylene  series;  and  the  isomers  of  the  acetylenes,  which 
have  two  double  bonds,  are  known,  by  analogy,  as  di-olefines. 
A  more  systematic  mode  of  naming  these  unsaturated  compounds 
is  to  use  the  ending  ene  to  indicate  the  ethylene  state  with  one 
double  bond,  diene  for  the  di-olefines  with  two  double  bonds, 
and  ine  for  compounds,  like  acetylene,  which  have  one  triple 
bond.  These  endings  are  added  to  the  stem  of  the  name  for  the 
paraffin  with  the  same  number  of  carbon  atoms.  Thus,  cor- 
responding to  ethane,  C2H6,  we  should  have  ethene,  C2H4,  and 
ethine,  C2H2;  and  in  the  next  group,  propane,  C3Hg;  propene, 
CH3.CH  :  CH2  ;  propadiene,  CH2  :  C  :  CH2;  and  propine,  CH3.C  :  CH. 


45 


UNSATURATED   HYDROCARBONS 


UNSATURATED   HYDROCARBONS 


Boiling 
Point 


Ethylene  Series 
CnHzn 

Ethylene,    CH2:CH2 -103° 

Propylene,  CH3.CH:  CH2.  ...  -48 
Butylene,  C2H5.CH:  CH2.. . .  -5 
Butylene,  CH3.CH:CH.CH3*  i 

Butylene,  (CH3)2C:  CH2..  .  .  -6 
Amylene,  C2H5CH:  CH.CH3  36 

Amylene,  (CH3)2CH.CH:CH2  20-21 
Amylene,  (CH3)  (C2H5)C:  CH2  3.1-32 
Amylene,  (CH3)2C:  CH.CH3  36-38 
Hexylene,  C4H9.CH:CH2  68-70 

Heptylene,  C5Hn.CH:CH2  96-99 
Octylene,  C6Hi3.CH:CH2  122-123 


Acetylene  Series         Boiling 
CnHjn_2  Point 

Acetylene,    CH :  CH -83.8° 

Allylene,    CH3.C:CH 

Dimethyl- 
Acetylene,  CH3.C  1C.  CH3.     27-28 
Ethyl- 
Acetylene,   C2H5.C :  CH.  .  1 8 
Methyl-Ethyl- 
Acetylene  C2H5.C:C.CH3     55-56 
Propyl- 

Acetylene  (n),C3H7.C :  CH    48-49 
Iso-Propyl- 
Acetylene,  (CH3)2CH.C •  H    28-29 


Cn  H2n  -  4  Series 
(CH3)2CH.CH2.CH:CH.C(CH3):C:CH2       Boils  I720-i76 


Diacetylene 
Dipropargyl 


Cn  HZn  -  e  Series 

CHiC.CiCH 

CHiC.CH2.CH2.CiCH 


85' 


Formation. — Various  unsaturated  hydrocarbons,  chiefly  ethy- 
lene  and  acetylene  are  formed  in  small  amounts  in  the  destructive 
distillation  of  organic  substances  and  are  consequently  found 
in  coal  gas.  They  are  formed,  theoretically,  by  the  removal  of 
pairs  of  hydrogen  atoms  from  the  paraffins: 

C2H6  -  2H  ->  C2H4  -  2H  -»  C2H2  -  2H  -*  2C 


These  changes  probably  occur  in  gas  retorts,  and  account  for 
the  large  percentage  of  hydrogen  (up  to  50  per  cent.)  and  the 
small  amounts  of  saturated  hydrocarbons  found  in  coal  gas,  as 
well  as  for  the  deposits  of  carbon  in  the  compact  form  of  "gas 
carbon,"  in  the  outlet  of  the  retorts. 

The  preparation  of  the  ethylene  hydrocarbons  may  be  effected: 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  46 

1.  By  removal  of  the  halogen  from  alkyl  dihalides  by  means  of 
a  metal  acting  on  an  alcoholic  solution: 

CH2Br.CH2Br  +  Zn  =  CH2:CH2  +  ZnBr2 

2.  By  heating  an  alkyl  monohalide  with  potassium  hydroxide 
in  an  alcoholic  solution: 

CH3.CH2Br  +  KOH  =  CH2  :CH2  +  KBr  +  H20 

(The  use  of  an  alcoholic  solution  of  the  hydroxide  is  important, 
since  in  aqueous  solution  the  presence  of  the  water  causes  the 
replacement  of  the  halogen  by  hydroxyl:  CH3.CH2Br  +  KOH  = 
CH3.CH2OH  +  KBr.) 

3.  From  alkyl  hydroxides  (alcohols)  by  withdrawing  the  ele- 
ments of  water: 

CH3.CH2OH  -  H2O  =  CH2:CH2 

This  may  be  effected  by  anhydrous  zinc  chloride,  phosphorus 
pentoxide,  syrupy  phosphoric  acid,  or  by  concentrated  sulphuric 
acid.  In  the  reaction  with  sulphuric  acid  intermediate  products 
are  formed. 

Ethylene  or  ethene,  C2H4.  Ethylene  is  usually  prepared  by 
heating  alcohol  with  about  six  times  its  weight  of  concentrated 
sulphuric  acid  to  about  170°.  (Syrupy  phosphoric  acid  may  be 
advantageously  substituted  for  sulphuric  acid.)  It  is  a  colorless 
gas  of  peculiar,  somewhat  sweetish  odor,  which  burns  with  a 
luminous  flame.  It  is  one  of  the  most  important  of  the  illu- 
minating constituents  of  coal  gas.  It  decomposes  at  about  400° 
with  the  production  of  hydrocarbons  of  the  paraffin,  acetylene, 
and  benzene  series.  By  the  electric  spark  discharge  it  is  decom- 
posed first  into  acetylene  and  hydrogen,  and  then  into  carbon 
and  hydrogen.  Reactions,  i.  Ethylene  combines  directly  with 
the  halogens,  most  energetically  with  chlorine  and  least  readily 
with  iodine. 

CH2:CH2  +  Br2  =  CH2Br.CH2Br 

Ethylene  Ethylene  bromide 


47  UNSATURATED  HYDROCARBONS 

In  chlorine  it  burns  with  a  smoky  flame.  2.  A  mixture  of  ethyl- 
ene  and  hydrogen  is  synthesized  to  ethane  at  about  300°  by 
finely  divided  nickel  as  contact  agent.  3.  Not  only  does  ethylene 
unite  with  the  halogens,  but  it  also  combines  additively  with 
hydrogen  bromide  and  iodide  forming  ethyl  halides: 

CH2:CH2  +  HBr  =  CH3.CH2Br 

Ethyl  bromide 

The  reaction  is  more  energetic  with  hydrogen  iodide  than 
with  hydrogen  bromide,  and  hydrogen  chloride  does  not  react 
at  all.  4.  With  hypochlorous  acid,  HC1O  (in  aqueous  solution), 
ethylene  combines  directly,  forming  monochlor- alcohol  or  ethyl- 
ene chlorhydrin: 

CH2:CH2  -f  HOC1  =  CH2C1.CH2OH 

Ethylene 
chlorhydrin 

We  shall  find  later  that  the  chlorhydrins  form  important  steps 
in  certain  syntheses.  5.  A  similar  reaction  occurs  between 
ethylene  and  sulphuric  acid,  ethylene  being  slowly  absorbed 
by  the  concentrated  acid  with  the  formation  of  ethyl  sulphuric 
acid  (cf.  p.  120): 

C2H4  +  H2SO4  =  (C2H6)HSO4 

Ethyl  sulphuric 
acid 

6.  Organic  acids  also  react  slowly  with  the  f  ormation  of  analogous 
compounds.  7.  Oxidizing  agents  act  on  ethylene  very  readily. 

This  description  of  the  properties  and  reactions  of  ethylene 
applies  in  a  general  way  to  the  other  members  of  the  series.  The 
first  of  these  "alkenes"  are  gases,  then  come  a  number  of  hydro- 
carbons which  are  liquids,  insoluble  in  water  but  soluble  in  alcohol 
and  in  ether.  The  higher  members  of  the  series  are  crystalline 
solids. 

Acetylene,  C2H2,  is  formed  in  small  amounts  when  an  electric 
arc  is  produced  between  carbon  poles  in  an  atmosphere  of  hydro- 
gen. This  gives  another  method  for  the  synthesis  of  organic  com- 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  48 

pounds  from  the  elements  (cf.  p.  26),  since  acetylene  is  readily 
converted  into  other  hydrocarbons  from  which  the  greatest 
variety  of  derivatives  can  be  made.  Acetylene  is  also  formed  as 
one  of  the  products  of  the  incomplete  combustion  of  other  hydro- 
carbons, which  occurs  when  the  supply  of  oxygen  is  limited.  The 
gases  that  come  from  a  Bunsen  burner,  when  the  flame  has 
"struck  back"  and  is  burning  at  the  bottom  of  the  tube,  contain 
acetylene,  though  in  small  amounts  (less  than  i  per  cent,  of  the 
gases).  Methods  of  formation  similar  to  those  given  for  ethyl- 
ene  may  be  employed  for  acetylene  and  its  homologues: 

CH2Br.CH2Br  +  2KOH  =  CH  i  CH  +  2KBr  +  2H2O 
CHBr2.CHBr2  +  2Zn  =  CH  I  CH  +  2ZnBr2 

But  since  the  manufacture  of  calcium  carbide  has  become  com- 
mercial, the  common  mode  of  preparation  is  through  the  reaction 
of  this  substance  with  water: 

C2Ca  +  2H2O  =  C2H2  +  Ca(OH)2 

This  may  be  regarded  as  another  elementary  synthesis;  for 
while  calcium  carbide  is  actually  made  from  lime,  CaO,  and  coke 
(C)  in  the  electric  furnace,  the  calcium  oxide  can  be  made  from 
the  metal  calcium  and  oxygen. 

Properties. — Acetylene  is  a  gas  of  garlic-like  odor.  When  made 
from  commercial  carbide  it  is  contaminated  with  small  amounts 
of  ill- smelling  gases,  such  as  phosphine,  and  hence  the  odor  of 
the  ordinary  gas  is  not  that  of  pure  acetylene.  It  burns  with  an 
exceedingly  bright  flame,  which  gives  much  smoke  unless  the  gas 
is  burnt  in  special  burners  whose  tips  deliver  about  one-half  of 
a  cubic  foot  per  hour.  It  can  be  liquefied  quite  readily  (by  a 
pressure  of  83  atmospheres  at  18°),  but  cannot  be  safely  used  in 
the  liquid  state  or  even  under  a  pressure  of  more  than  two  at- 
mospheres, since  under  these  circumstances  it  is  liable  to  explode 
violently  with  the  production  of  hydrogen  and  finely  divided 
carbon.  This  instability  indicates  that  acetylene  possesses  an 


49  UNSATURATED  HYDROCARBONS 

unusual  amount  of  stored  or  potential  energy.  It  is  in  fact  an 
endothermic  compound  which  absorbs  58.7  calories  in  its  forma- 
tion (cf.  p.  53).  It  is  slightly  soluble  in  a  number  of  liquids,  and 
dissolves  quite  freely  in  acetone  (24  vols.  of  acetylene  in  i  vol. 
acetone  under  atmospheric  pressure)  forming  a  solution  in  which, 
even  under  considerable  pressure,  it  is  not  explosive.  Such 
solutions  are  used  as  a  convenient  source  of  the  gas  for  lighting 
purposes.  Otherwise  it  is  generated  as  it  is  used,  as  in  bicycle 
and  automobile  lamps,  or  is  stored  in  small  gas  holders  under  slight 
pressure  for  household  lighting.  Mixtures  of  acetylene  and  air 
are  explosive  through  a  remarkably  wide  range  of  proportions: 
beginning  with  only  3.5  per  cent,  of  acetylene  by  volume  and  end- 
ing with  82  per  cent.  For  comparison  it  may  be  stated  that  the 
range  for  hydrogen  is  from  5  to  72  per  cent.;  for  carbon  monoxide, 
*3  to  75  per  cent.;  for  water  gas,  9  to  55  per  cent;  coal  gas,  6  to 
29  per  cent. ;  and  for  methane,  5  to  13  per  cent. 

When  acetylene  is  passed  through  a  tube  heated  to  dull  red- 
ness, it  "polymerizes"  by  the  union  of  its  molecules,  and  forms, 
among  other  compounds,  benzene,  CeH6,  which  is  the  most  im- 
portant hydrocarbon  of  the  aromatic  series. 

Acetylene  and  its  homologues  unite  additively  with  the  halo- 
gens, with  hydrogen  (in  the  presence  of  platinum  black),  and  with 
the  halogen  acids.  They  are  readily  oxidized  by  oxidizing  agents  in 
solution  (e.g.,  KMnO^,  showing  reactions  which  are  analogous 
to  those  of  ethylene  and  its  homologues.  All  compounds  of  the 
acetylene  series  that  have  a  triple  bond  between  two  carbon 
atoms  at  the  end  of  the  chain  give  a  distinctive  reaction  with 
ammoniacal  solutions  of  silver  or  cuprous  chloride.  This  con- 
sists, in  the  case  of  acetylene,  in  the  precipitation  of  carbides  of 
these  metals,  C2Ag2  and  C2Cu2,  compounds  in  which  the  metal 
has  taken  the  place  of  the  hydrogen  of  the  acetylene,  and  which 
are  consequently  called  "  acetylides."  When  dry,  these  com- 
pounds explode  when  struck  or  when  heated  to  100°.  With 
hydrochloric  acid,  copper  acetylide  gives  acetylene. 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  50 

CH2  =  C  -  CH  =  CH2, 


Of  the  di-olefines,  isoprene,  CsHs  or 

CH3 

is  of  special  interest,  because  of  the  recent  discovery  that  it  can 
be  converted  into  India  rubber.  Isoprene  is  a  liquid,  boiling  at 
37°.  It  is  one  of  the  products  of  the  destructive  distillation  of 
rubber,  and  is  formed  when  turpentine  is  passed  through  a  red 
hot  tube.  Its  conversion  into  India  rubber  is  the  effect  of  a 
polymerization,  or  union  of  several  molecules  to  a  more  com- 
plex one  of  the  same  composition. 

Hydrocarbons  of  the  Formulas,  CnH2n-4,  CnH2n-6.  The 
compound  of  the  lowest  molecular  weight  corresponding  to  the 
general  formula  CnH2n-4  which  is  theoretically  possible  would  be 
C4H4,  and  this  might  have  the  structure  CH2:C:C:CH2  or 
CH;  C.CH:  CH2.  The  higher  members  of  the  series  would  have 
similar  constitutions  with  either  three  double  linkages  or  one 
double  and  one  triple  linkage,  on  the  assumption  that  the  carbon 
atoms  of  each  compound  form  open  chains.  One  such  hydro- 
carbon with  three  double  bonds  has  been  obtained  by  the  with- 
drawal of  the  elements  of  water  from  the  natural  di-olefine  alcohol 
geraniol  (p.  87)  and  has  the  formula  (CH3)2CH.CH2.CH:CH?- 
C(CH3):C:CH2  =  CioHi6.  This  hydrocarbon  unites  additively 
with  six  atoms  of  hydrogen  or  of  bromine  with  the  formation  of 
saturated  compounds,  CioH22  and  CioHi6Br6.  Other  open-chain 
hydrocarbons  of  this  series  are  practically  unknown. 

A  large  number  of  hydrocarbons  known  as  terpenes  which 
occur  in  the  vegetable  kingdom  have  the  same  composition,  but 
are  proved  to  be  cyclic  compounds  in  which  the  carbon  atoms 
form  closed  chains  or  rings  (p.  257). 

In  the  series  of  open-chain  hydrocarbons  of  the  formuia 
CnH2n_6  the  simplest  is  diacetylene,  CHiC.C-CH,  which  can 
be  made  from  propiolic  acid  (p.  in),  CHlC.CO.OH,  through  di- 
acetylene-dicarboxyKc  acid,  CO.OH.CiC.C-C.CO.OH.  Dipro- 
pargyl,  CHlC.CH2.CH2.GCH,  =  C6H6,  can  be  made  from  the 


51  UNSATURATED  HYDROCARBONS 

tetrabromide  of  diallyl,  CH2Br.CHBr.CH2.CH2.CHBr.CH2Br, 
by  splitting  off  hydrogen  bromide  by  means  of  alcoholic  potassium 
hydroxide.  This  mode  of  formation  and  its  acetylene-like  proper- 
ties establish  its  constitution  as  given  in  the  formula.  This 
hydrocarbon  is  of  especial  interest  because  it  is  isomeric  with 
benzene,  the  most  important  of  the  cyclic  hydrocarbons.  It  is 
a  liquid  boiling  at  about  85°,  having  a  specific  gravity  of  0.8 1. 
It  slowly  changes  to  a  shellac-like  mass,  which  decrepitates  when 
heated. 

No  open-chain  hydrocarbons  with  more  than  three  double  or 
two  triple  linkages  are  definitely  known. 

Heats  of  Combustion  and  of  Formation 

Knowledge  of  the  amount  of  heat  which  is  produced  by  a  given 
weight  of  a  substance  used  for  fuel,  such  as  the  different  kinds  of 
coal,  petroleum,  water  gas,  and  coal  gas,  is,  of  course,  of  practical 
importance. 

Since  the  gaseous  and  liquid  fuels  are  composed  largely  of  hydro- 
carbons, the  heating  value  of  individual  hydrocarbons  as  well  as 
that  of  the  hydrogen  and  carbon  monoxide,  which  are  usually 
present  in  fuel  gases,  is  also  important.  To  the  chemist,  the 
heating  value  of  these  compounds  is  of  'special  interest,  because 
by  its  aid  he  can  find  the  "heat  of  formation"  of  the  compounds, 
which  gives  information  in  regard  to  their  stability  and,  to  some 
extent,  to  their  reactivity  with  other  compounds. 

It  is  assumed  that  the  student  is  familiar  with  the  units  of  heat 
measurement,  the  small  or  gram-calorie  and  the  large  or  1000 
gram-calorie.  The  latter  is  used  in  the  following  discussion. 

By  the  heat  of  formation  is  understood  the  number  of  heat  units 
which  are  given  out  or  absorbed  in  the  formation  of  a  gram- 
molecular  weight  of  the  compound  from  its  elements.  This  is 
readily  determined  when  the  compound  can  be  made  by  the  direct 
union  of  its  elements,  as  in  the  case  of  water,  carbon  dioxide, 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  52 

etc.,  but  in  other  cases  it  must  be  arrived  at  by  an  indirect  method. 
The  method  depends  on  the  fact  that  the  same  amount  of 
energy  is  required  to  separate  the  elements  of  a  compound  as 
is  set  free  in  their  union.  The  product  of  a  reaction  which  is  at- 
tended with  the  production  of  heat — an  exothermic  reaction — has 
less  potential  energy  and  hence  greater  stability  in  proportion  to 
the  amount  of  heat  evolved,  and,  similarly,  the  instability  of  a 
compound  is  greater  the  greater  the  heat  which  is  absorbed  in 
its  formation,  and  the  greater  the  potential  energy  which  it 
therefore  possesses. 

Now,  the  heat  of  formation  of  a  compound  must  be  equal  to  the 
heat  which  its  elementary  constituents  would  produce  on  oxida- 
tion, less  the  heat  of  combustion  of  the  compound.  For  the 
amount  of  energy  which  is  necessary  to  break  the  union  of  the 
elements  will  fail  to  appear  as  heat  when  the  compound  is  burned. 
If,  therefore,  we  know  the  heats  of  combustion  of  the  con- 
stituent elements  and  of  the  compound,  the  heat  of  formation  is 
their  difference.  In  the  table  are  given  the  heats  of  combustion 
and  of  formation  of  a  number  of  hydrocarbons  which  we  have 
been  studying,  as  well  as  those  of  their  constituents,  carbon  and 
hydrogen.  For  use  in  determining  the  heats  of  formation  both 
are  given  for  \the  gram-molecular  weight  of  the  compounds,  but 
in  the  first  column,  the  heats  of  combustion  for  one  gram  are  also 
given  as  is  usual  in  the  practical  evaluation  of  fuel  substances. 

HEAT  OF 
FORMATION 
One  Gram- 
molecule 

Hydrogen 
Carbon 

Paraffins 

CH4  13.3  213.5  18.5 

158-8 
C2H«  12.4  372.3  22-7 

156.1 
C3H8  12.0  528.4  29.6 


HEAT  OF  COMBUSTION 

One  Gram- 

One  Gram 

molecule 

34-2 

69.0 

7.83 

94.0 

Difference 

13-3 

213-5 

158.8 

12.4 

372.3 

156.1 

12.0 

528.4 

158.8 

S3 


UNSATURATED   HYDROCARBONS 


Paraffins 
C4H10 


HEAT  OF  COMBUSTION 

One  Gram- 
One  Gram  molecule  Difference 

ii. 8 


HEAT  OF 
FORMATION 
One  Gram- 
molecule 


II. 7 


Unsaturated 
Hydrocarbons 

C2H4 


C3H6 

C4H8 
C2H2 

C3H4 


687.2 
847.1 

341. 1 
499-3 

650.6 
315.7 

473-6 


33.8 


159-9 


158.2 


157-9 


-10.3 

1.4 

-58.7 

-53.6 


It  will  be  noticed  that  while  the  heat  of  combustion  for  the  same 
weight  of  different  hydrocarbons  decreases  as  the  molecular 
weights  increase,  the  figures  for  the  gram-molecular  quantities 
show  a  fairly  constant  increase  of  about  158  calories  for  each 
addition  of  CH2. 

We  may,  therefore,  reckon  the  gram-molecular  heat  of  combus- 
tion for  any  hydrocarbon  if  we  know  what  it  is  for  one  member  of 
an  homologous  series.  For  instance,  knowing  the  heat  of  combus- 
tion of  methane  (213.5)  we  may  ^u^-  that  °^  CnH24  as  ^o^ows: 
CnH24  =  CH4  +  ioCH2;  hence,  213.5  +  (I0  X  158)  =  1793-5 
which  is  the  gram- molecular  heat  of  combustion  of  CnH24-  As 
this  is  the  heat  from  156.192  grams  (gram-molecular  weight)  of 
undecane,  the  heat  obtainable  from  one  gram  would  be  1793.5  + 
156.192  =  11.48  cal. 

To  find  the  heat  of  formation  of  a  hydrocarbon,  the  procedure 
is  as  follows:  Ethane  has  as  its  heat  of  combustion  372.3  cal. 
The  gram-molecule  of  ethane  contains  24  grams  of  carbon  and 
3  g-mols.  of  hydrogen,  and  the  heat  which  would  be  developed 
by  burning  these  amounts  of  carbon  and  hydrogen  is  7.83  X  24  = 
1 88  cal.  and  69  X  3  =  207,  or  in  all,  395;  the  heat  of 


INTRODUCTION  TO   ORGANIC  CHEMISTRY  54 

formation  of  ethane  is,  therefore,  395  —  372.3  =  22.7  cal.  For 
acetylene  (7.83  X  24)  +  (69  X  i)  -  315.7  =  -  58.7  cal- 
ories. (For  further  discussion  of  thermochemistry  the  student 
is  referred  to  a  Physical  Chemistry. 

Halogen  Derivatives  of  Unsaturated  Hydrocarbons 

There  are  two  types  of  these  derivatives  which  are  quite  dif- 
ferent in  then*  behavior:  those  in  which  the  halogen  is  united  to 
an  unsaturated  carbon  atom,  one  that  is  linked  to  another  carbon 
atom  by  a  double  or  triple  bond,  as  CH2:CHBr,  or  CIiC.CH3; 
and  those  where  the  halogen  is  joined  to  a  saturated  carbon 
atom,  or  one  linked  to  another  carbon  atom  by  a  single  bond, 
as  CH2:CH.CH2Br  or  CHiC.CH2Cl. 

In  compounds  of  this  second  type,  the  halogen  is  readily  re- 
placed by  hydroxyl,  cyanogen,  and  other  groups  as  in  the  case  of 
the  alykl  halides;  while  with  halogen  derivatives  of  the  first  type 
these  reactions  do  not  take  place,  i.  Compounds  of  the  first 
type  where  the  halogen  is  united  to  a  carbon  atom  with  a  double 
bond  may  be  made  by  the  action  of  alcoholic  potassium  hydroxide 
on  dihalogen  derivatives  of  the  saturated  hydrocarbons: 

CH2Br.CH2Br  +  KOH  =  CH2  :CHBr  +  KBr  +  HOH 

Ethylene  bromide  Vinyl  bromide 

CH3.CH2.CHC12  +  KOH  =  CH3.CH:CHC1  +  KC1  +  H2O 

Propylidene  chloride  Chlorpropylene 

Their  formation  also  takes  place  by  direct  addition  of  the  hydro- 
gen halide  to  hydrocarbons  of  the  acetylene  series: 

CH  :  CH+HBr  =  CH2 :  CH£r 

But  with  another  molecule  of  the  hydrogen  halide  this  gives  an 
alkyl  dihalide: 

CH2:CHBr  +  HBr  =  CH3.CHBr2 


55  UNSATURATED  HYDROCARBONS 

Vinyl  chloride,  CH2 :  CHC1,  is  a  gas;  the  bromide,  CH2 :  CHBr, 
is  a  liquid  of  ethereal  odor,  boiling  at  16°;  vinyl  iodide,  CH2 :  CHI, 
is  also  a  liquid,  which  boils  at  56°.  The  chloride  and  bromide 
change  to  white  solids  when  exposed  to  sunlight,  being  "poly- 
merized" (several  molecules  combined  to  one).  Reagents  such 
as  potassium  hydroxide,  sodium  ethylate,  or  sodium  acetate  do 
not  give  substitution  products,  but  cause  the  compounds  to  break 
down  into  acetylene  and  the  halogen  acid.  The  hydrocarbon 
radical,  CH2:CH  — ,  in  these  compounds  is  called  vinyl  and  ap- 
pears in  other  derivatives. 

Bromacetylene,  CBr-CH,  is  made  from  bromethylene  by 
means  of  alcoholic  potash: 

CHBr: CHBr  -  HBr  =  CBr-CH 

Bromacetylene  is  a  gas  which  condenses  to  a  liquid  in  a  freez- 
ing mixture,  and  polymerizes  to  a  solid  in  the  light.  lodoace- 
tylene.  CI  i  CH,  is  a  crystalline  solid,  of  disagreeable  odor,  and 
apparently  very  poisonous. 

2.  Compounds  of  the  second  type  in  which  the  halogen  is 
united  to  a  saturated  carbon  atom  have  the  characteristics  both 
of  unsaturated  hydrocarbons  and  of  alkyl  halides.  The  best 
known  halogen  compounds  of  this  class  are  obtained  from  allyl 
alcohol,  CH2:CH.CH2OH,  and  from  propargyl  alcohol,  CHi  C.- 
CH2OH  (cf.  p.  69),  by  the  action  of  phosphorus  halides.  Allyl 
chloride,  CH2 :  CH.CH2C1,  and  the  corresponding  allyl  bromide 
and  iodide  are  liquids  boiling  at  46°,  70°,  and  103°,  respectively. 
They  have  an  odor  resembling  that  of  mustard.  The  propargyl 
halides  are  also  liquids  and  give  metallic  derivatives  such  as  are 
characteristic  of  the  acetylene  grouping. 

The  reactions  on  page  54  show  how  various  saturated  and 
unsaturated  halogen  derivatives  may  be  made  from  each  other. 
The  splitting  off  of  halogen  and  hydrogen  by  alcoholic  alkali,  and 
the  addition  of  halogens  or  hydrogen  halides  to  the  resulting 
unsaturated  compounds  give  means  for  making  halogen  deriva- 


INTRODUCTION    TO    ORGANIC    CHEMISTRY  56 

tives  of  almost  any  type.  From  ethyl  bromide,  for  instance,  all 
possible  halogen  derivatives  of  ethane,  ethylene,  and  acetylene, 
as  well  as  ethylene  and  acetylene  themselves,  may  be  obtained: 

-  HBr  +  Br2  -  HBr 

CH3.CH2Br >     CH2:CH2    >  CH2Br.CH2Br-     — » 

-f  Br2  -  HBr  +  Br2 

CHBr:CH2 >  CHBr2.CH2Br >      CBr2:CH2     > 

-  HBr  +  Br2  -  HBr 

CBr3.CH2Br >    CBr2:CHBr >    CBr3.CHBr2   -    > 

CBr2.CBr2     _±^    CBr3.CBr3. 


CHAPTER  V 

THE   ALCOHOLS— HYDROXYL    DERIVATIVES    OF    THE 
ALIPHATIC  HYDROCARBONS 

Among  the  many  organic  compounds  which  contain  hydrogen 
and  oxygen,  there  are  several  important  groups  of  substances, 
the  members  of  each  of  which  show  general  characteristics,  and 
a  similarity  in  behavior  such  as  marks  the  different  series  of 
hydrocarbons  which  we  have  studied;  and  we  shall  find  here, 
as  in  the  case  of  the  hydrocarbons,  that  the  members  of  ea.ch 
group  form  an  homologous  series,  with  a  general  formula. 

One  of  these  groups  is  that  of  the  alcohols,  of  which  the  well- 
known  "wood  alcohol"  and  ordinary  alcohol  are  the  most  im- 
portant members.  These  two  alcohols  will  now  be  studied  as 
typical  of  the  group. 

Formula  of  an  Alcohol. — Neither  of  the  commercial  alcohols 
is  quite  pure,  or  free  from  water,  but  the  anhydrous  pure 
alcohols  can  be  obtained  from  them.  Pure  wood  alcohol  is  a 
liquid  boiling  at  66°.  Its  percentage  composition  is  C  =  37.46, 
H  =  12.59,  O  =  49.95,  and  its  vapor  density  is  1.106  (air  =  i); 
hence  the  molecular  formula  is  CH4O.  From  the  corresponding 
data  for  ordinary  alcohol,  its  formula  is  found  to  be  C2H«O. 
It  is  impossible,  with  tetravalent  carbon,  to  write  graphic  formulas 
for  these  alcohols  in  which  the  oxygen  is  united  by  both  of  its 
valencies  with  a  carbon  atom.  For  CH4O,  only  one  graphic 

H 

formula  can  be  written,  namely,  H —  C  — O — H,  in  which  the 

H 

57 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  58 

oxygen  atom  and  one  hydrogen  atom  form  a  hydroxyl  group. 
For  C2H6O  there  are  two  arrangements  which  account  for  the 

H     H  H  H 

II  II 

valencies,  H— C— C— O— H  and    H— C— O— C— H.      The 

II  II 

H     H  H  H 

first,  containing  an  hydroxyl  group,  would  seem  the  more  prob- 
able, because  of  the  similarities  in  the  properties  of  the  two  alcohols. 
The  matter  can,  however,  be  settled  in  the  following  manner: 
Anhydrous  alcohol  acts  on  sodium  with  the  evolution  of  hydrogen 
and  the  formation  of  a  compound  whose  formula  is  found  to  be 
C2H5NaO,  in  which  sodium  has  replaced  one  atom  of  hydrogen 
in  the  alcohol  molecule.  As  no  other  compound  containing  a 
larger  proportion  of  sodium  can  in  any  way  be  produced  from 
alcohol  and  sodium,  we  conclude  that  one  of  the  six  hydrogen 
atoms  in  alcohol  stands  in  a  different  relation  from  the  other  five. 
This  can  only  be  accounted  for  by  the  first  of  the  two  possible 
formulas,  and  decides  in  its  favor  as  the  one  which  represents 
the  constitution  of  alcohol.  This  conclusion  is  confirmed  by 
the  result  of  the  reaction  which  alcohol  undergoes  with  phos- 
phorus chlorides: 

C2H60  +  PC15  =    C2H5C1  +  POC13  +  HC1 
3C2H6O  +  PC13  =  3C2H5C1  +  H3P03 

The  formula  of  the  chlorin,e  substitution  product  is  determined 
in  the  usual  way  and  shows  that  one  atom  of  chlorine  has  taken 
the  place  of  the  oxygen  and  one  hydrogen  atom;  and  this  clearly 
indicates  that  these  two  atoms  were  acting  as  the  monovalent 
group  hydroxyl.  Wood  alcohol  gives  exactly  similar  reactions, 
and  therefore  we  consider  these  alcohols  to  be  alkyl  hydroxides. 
They  can,  in  fact,  be  made  by  a  reaction  which  this  view  of 
their  character  suggests,  namely,  by  the  reaction  of  the  alkyU 


59  THE   ALCOHOLS 

halides  with  potassium  hydroxide  in  aqueous  solution,  or  with 
silver  hydroxide  (p.  34) : 

CH3I  +  KOH  =  CH3OH  +  KI 
C2H5Br  +  KOH  =  C2H5OH  +  KBr 

(Compare  these  reactions  with  those  which  occur  between 
the  alkyl  halides  and  potassium  hydroxide  in  alcoholic  solutions 
(p.  46). 

Finally,  all  the  facts  that  we  know  about  these  compounds 
agree  with  this  conclusion  that  they  are  hydroxyl  derivatives  of 
the  hydrocarbons,  and  all  other  such  compounds  are  grouped  with 
them  as  alcohols.  The  general  formula  of  an  alcohol  is,  there- 
fore, CnH2n  +  iOH. 

Methyl  alcohol,  CH3OK,  commercially  known  as  "wood 
alcohol,"  is  one  of  the  products  of  the  destructive  distillation  of 
wood.  The  process  is  carried  out  in  iron  retorts,  and  yields  first 
a  watery  distillate  called  "pyroligneous  acid,"  and  then  gases 
(methane,  ethane,  ethylene,  carbon  dioxide,  etc.)  and  tar,  leav- 
ing a  residue  of  charcoal  in  the  retort.  The  pyroligneous  acid 
contains  methyl  alcohol,  acetic  acid,  and  acetone  in  aqueous 
solution,  together  with  smaller  amounts  of  many  other  substances. 
The  yield  of  the  various  products  depends  on  the  kind  of  wood 
used,  and  also  on  the  manner  of  heating.  Quick  heating  to  a 
high  temperature  gives  the  greatest  amount  of  gas,  and  prolonged 
heating  at  lower -temperatures  increases  the  proportion  of  pyro- 
ligneous acid  and  tar.  From  birch,  beech,  and  oak  about  30 
per  cent,  of  the  weight  of  the  wood  is  obtained  in  the  watery 
distillate.  Of  this  about  10  per  cent,  is  acetic  acid,  i  per  cent, 
methyl  alcohol,  and  o.i  per  cent,  acetone.  On  distilling  the 
pyroligneous  acid,  the  alcohol  and  acetone,  whose  boiling  points 
are  not  very  far  apart  and  much  lower  than  that  of  acetic  acid, 
are  separated  from  the  latter,  the  separation  being  often  made 
more  complete  by  passing  the  vapors  through  milk  of  lime  which 
fixes  the  acid  as  calcium  acetate. 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  60 

A  second  distillation  from  quicklime  gives  an  alcohol  of  99 
per  cent.,  which  still  contains  some  acetone.  This  is  not  ob- 
jectionable for  most  of  the  commercial  uses  of  the  alcohol.  The 
alcohol  may  be  obtained  in  a  state  of  purity  as  follows.  By  add- 
ing anhydrous  calcium  chloride  to  the  impure  alcohol  a  crystalline 
compound  is  formed  in  which  the  alcohol  plays  the  part  of 
"water  of  crystallization."  When  this  is  heated  to  100°,  the 
volatile  impurities  are  driven  off,  and  then,  on  adding  water,  the 
pure  alcohol  is  distilled.  Absolutely  pure  methyl  alcohol  may  be 
obtained  from  the  methyl  ester  of  oxalic  acid  (p.  179),  by  boiling  it 
with  water.  The  disagreeable  odor  of  most  commercial  wood 
alcohol  is  due  to  impurities;  the  pure  alcohol  has  only  a  slight 
odor  resembling  that  of  ethyl  alcohol. 

Ethyl  alcohol,  CH3.CH2OH,  commercially  known  as  grain  alco- 
hol and  ordinarily  as  "alcohol,"  is  the  chief  product  of  the  ordin- 
ary fermentation  of  certain  sugars.  This  fermentation  is  brought 
about  in  the  technical  manufacture  of  alcohol  by  the  addition  of 
yeast,  and  it  occurs  naturally  in  the  sweet  juices  of  fruits,  such  as 
grapes,  apples,  etc.,  and  in  sugar  solutions  which  are  exposed  to 
the  air,  because  of  the  almost  universal  presence  of  yeast  spores 
in  the  atmosphere.  Much  alcohol  is  produced  from  molasses 
(p.  213);  and  much  has  its  source  in  the  starch  of  various  grains 
such  as  maize,  rye,  etc.  in  the  United  States,  while  in  Europe  the 
starch  of  potatoes  is  used.  The  starch  is  first  converted  into 
fermentable  sugars,  and  yeast  is  then  added  to  their  solutions. 
Alcohol  has  also  been  made  to  some  extent  from  saw-dust  (cellu- 
lose) from  which  a  fermentable  sugar  can  also  be  obtained.  The 
conversion  of  starch  and  cellulose  into  sugars  and  the  fermenta- 
tion of  the  latter  are  discussed  in  a  later  chapter.  It  is  sufficient 
here  to  note  that  the  fermentation  requires  a  rather  dilute  solution 
of  the  sugars,  and  that  the  immediate  product  contains  not  more 
than  about  12  per  cent,  of  alcohol  in  aqueous  solution,  and  in  the 
case  of  cider,  wines  and  beer,  often  much  less.  No  alcoholic 
solution  containing  more  than  about  14  per  cent,  of  alcohol  can 


6 1  THE   ALCOHOLS 

be  obtained  by  fermentation  alone,  since  alcohol  of  this  strength 
inhibits  the  fermentation.  When  the  purpose  of  the  fermentation 
is  to  produce  such  beverages  as  those  just  named,  no  distillation  is 
necessary;  but  for  making  liquors  such  as  whiskey,  brandy,  rum, 
etc.,  or  for  the  preparation  of  commercial  alcohol,  the  dilute  solu- 
tion is  distilled  with  the  production  of  stronger  alcoholic  solutions. 

The  wines,  beers,  etc.,  are,  therefore,  dilute  alcoholic  solutions 
which  contain  various  amounts  of  substances  extracted  from 
the  materials  out  of  which  they  are  made,  and  which  give  them 
their  "body,"  flavor,  and  color;  while  the  distilled  liquors  are, 
of  course,  freed  from  all  non-volatile  substances,  and  are  solu- 
tions containing  40-60  per  cent,  of  alcohol,  with  minute  amounts 
of  volatile  matters  which  impart  an  aroma  and  taste  depending 
on  the  original  material  employed.  In  some  instances,  as  in 
gin,  a  peculiar  taste  and  odor  are  imparted  by  the  addition  of 
aromatic  substances  before  the  distillation.  The  distillates  are 
all  colorless,  and  the  color  which  many  liquors  have  is  given 
them  by  standing  in  casks  of  charred  wood  as  in  the  case  of  some 
whiskeys,  or  by  addition  of  caramel,  etc.  Brandies  are  made 
by  distilling  wine  or  the  fermented  juices  of  various  fruits,  such 
as  apples,  peaches,  etc.;  whiskey  is  made  from  Indian  corn  or 
rye;  rum,  from  molasses. 

For  the  preparation  of  commercial  alcohol,  a  more  efficient 
apparatus  is  employed  for  the  separation  of  the  alcohol  and  water 
by  distillation  than  that  used  in  making  the  distilled  liquors, 
with  the  result  that  there  is  only  about  4  per  cent,  of  water  in 
the  distillate.  The  rectification  cannot  go  farther  than  this, 
since  96  per  cent,  of  alcohol  and  4  per  cent,  of  water  form  a  mix- 
ture which  has  a  constant  boiling  point  under  ordinary  pressure. 
Commercial  alcohol  is  usually  from  93-95  per  cent. 

In  order  to  get  anhydrous  alcohol  it  is  necessary  to  use  some 
dehydrating  agent.  By  allowing  95  per  cent,  alcohol  to  stand 
in  contact  with  quicklime  for  some  time  and  then  distilling,  most 
of  the  water  is  retained  by  the  lime  in  the  form  of  calcium 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  62 

hydroxide,  and  the  distillate  does  not  contain  more  than  0.5 
per  cent. 

This  is  often  called  "absolute  alcohol,"  though  the  name  prop- 
erly belongs  only  to  a  perfectly  water-free  product.  The  last 
amounts  of  water  can  be  removed  by  means  of  anhydrous  copper 
sulphate  or  by  sodium  or  calcium.  It  is,  however,  very  difficult 
to  keep  alcohol  free  from  water,  as  it  is  very  hygroscopic  and  takes 
up  water  from  ordinary  air.  Traces  of  water  are  detected  by 
the  blue  color  which  white  anhydrous  copper  sulphate  assumes 
when  shaken  with  the  alcohol,  or  by  the  yellow  color  imparted 
to  the  alcohol  when  barium  oxide  is  added  (barium  oxide  dis- 
solves only  in  anhydrous  alcohol). 

Properties. — Methyl  alcohol  boils  at  66°,  ethyl  alcohol  at  78°. 
Both  mix  with  water  in  all  proportions  and  the  mixing  is  attended 
with  a  rise  in  temperature  and  a  contraction  in  volume.  Both 
are  solvents  of  wide  application  and  burn  with  a  hot,  almost 
colorless  flame.  Both  are  intoxicating,  and  are  poisonous,  at 
least  when  pure  or  but  slightly  diluted.  The  poisonous  char- 
acter of  methyl  alcohol  is  much  more  pronounced  than  that  of 
ethyl  alcohol,  and  prolonged  exposure  to  its  vapor  is  attended 
with  serious  consequences,  and  has  been  followed  by  loss  of  sight. 
On  this  account  ethyl  alcohol  is  preferable  as  a  solvent  and  has 
largely  displaced  wood  alcohol  in  making  shellac  varnish  since 
the  introduction  of  the  tax-free  "  denatured  alcohol,"  which  is 
ordinary  alcohol  rendered  unfit  for  internal  use  by  the  addition  of 
wood  alcohol,  benzene,  and  various  other  substances.  "  Proof 
spirit"  contains  50  per  cent,  of  alcohol  by  volume.  The  amount 
of  alcohol  in  pure  aqueous  solutions  is  found  by  determining  the 
density  and  using  "alcohol  tables"  that  give  the  percentages  of 
alcohol  corresponding  to  the  densities. 

Reactions. — Both  alcohols  are  neutral  substances.  They 
undergo  the  following  reactions,  i .  The  hydrogen  of  the  hydroxyl 
group  is  replaced  by  sodium,  which  acts  on  the  alcohols  much 
more  moderately  than  on  water.  The  alcoholates  thus  formed  are 


63  THE   ALCOHOLS 

solid  substances  which  crystallize  with  "alcohol  of  crystalliza- 
tion" (e.g.,  C2H5ONa.2C2H6OH),  which  can  be  removed  by  heat- 
ing. The  alcoholates  of  sodium  and  potassium  are  decomposed 
by  water* 

C2H6ONa  +  HOH  +±  C2H5OH  +  NaOH 

The  reaction  is  reversible  to  some  extent,  and  hence  a  solution 
of  sodium  hydroxide  in  alcohol,  such  as  is  employed  in  some 
organic  reactions  (cf.  p.  46),  contains  some  alcoholate.  Since 
the  alcohols  react  only  with  the  most  positive  metals,  and  no 
alcoholates  of  such  metals  as  zinc  or  silver  can  be  made,  these 
compounds  cannot  be  regarded  as  salts  in  the  proper  sense  of  the 
term,  but  rather  as  mixed  alkyl  and  metal  oxides,  and  the 
names  of  sodium  methoxide  and  ethoxide  are  therefore  preferable 
to  the  salt-suggesting  term  alcoholate. 

2.  The  alcohols  show  a  certain  analogy  to  the  inorganic  bases 
by  reacting,  as  these  do,  with  acids  with  the  production  of  water 
and  compounds  in  which  the  hydroxyl  group  of  the  alcohol  is 
replaced  by  acid  radicals: 

C2H5OH  +  HC1  *±  C2H5C1  +  H2O 
CH3OH  +  H2SO4  ^  CH3.H.SO4  +  H2O 

Similar  reactions  take  place  between  the  alcohols  and  organic 
acids,  and,  since  they  are  reversible  reactions,  are  in  all  cases 
furthered  by  an  excess  of  the  acid  or  by  the  presence  of  some 
water-withdrawing  substance.  The  compounds  formed  with 
acids,  while  not  well-defined  salts,  show  some  marked  analogies 
to  salts,  and  are  called  "ethereal  salts"  or  esters  (cf.  p.  119). 

3.  The  characteristic  action  of  the  phosphorus  halides  on  alco- 
hols, resulting  in  the  replacement  of  the  hydroxyl  group  by  the 
halogen,  has  been  given  (p.  32). 

4.  By  means  of  water-absorbing  agents,  such  as  zinc  chloride 
or  concentrated  sulphuric  acid,  the  elements  of  water  may  be 
withdrawn  from  alcohols  with  the  production  of  unsaturated 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  64 

hydrocarbons  or  of  ethers.  Methyl  alcohol,  however,  can  yield 
n«  unsaturated  hydrocarbon,  though  it  gives  an  ether.  When 
sulphuric  acid  is  used,  the  alkyl  sulphuric  acid  is  first  formed 
(e.g.,  C2H5.HSO4),  and  then  this  breaks  up  at  170°  or  180°  in 
the  presence  of  a  large  excess  (5:1)  of  concentrated  acid  into  sul- 
phuric acid  and  the  alkene: 

C2H5.HSO4  =  C2H4  +  H2S04 

Under  other  conditions  (i3o°-i4o°  and  a  smaller  proportion 
(1.5:  i)  of  acid),  ethers  or  alkyl  oxides  are  formed  (cf.  p.  70): 

C2H5.HSO4  +  C2H5OH  =  (C2H5)2O  +  H2S04 
similarly: 

C2H5I  +  C2H5OH  =  (C2H5)20  +  HI 

5.  Alcohols  are  not  only  readily  burned  to  carbon  dioxide  and 
water,  but  are  also  easily  oxidized  in  dilute  solution  to  inter- 
mediate compounds.1 

By  means  of  a  mixture  of  dichromate  of  potassium  and  dilute 
sulphuric  acid,  for  instance,  ethyl  alcohol  is  oxidized  as  follows: 

C2H5OH  +  O  -»  C2H4O  (aldehyde) 
and  C2H4O  +  O  =  C2H4O2 (acetic  acid) 

The  higher  homologues  of  ethyl  alcohol  give  similar  reactions, 
but  methyl  alcohol  is  oxidized  much  more  readily  than  the  other 
alcohols  so  that  the  reaction  hurries  through  the  aldehyde  to  the 
acid  and  even  to  the  end  products,  carbon  dioxide  and  water. 
The  vapor  of  methyl  alcohol  mixed  with  air  is,  however,  partially 
oxidized  to  the  corresponding  aldehyde  when  brought  in  contact 
with  a  heated  spiral  of  platinum  wire.  These  reactions  will 
be  discussed  in  connection  with  our  study  of  the  aldehydes, 
ketones,  and  acids. 

6.  Chlorine  acts  on  alcohols  first  as  an  indirect  oxidizing  agent 

1  The  oxidizing  agents  usually  employed  in  organic  chemistry  are  nitric 
acid,  chromic  acid  (K2Cr2O7  +  H2SO4),  potassium  permanganate,  manganese 
dioxide  and  sulphuric  acid,  and,  occasionally,  chlorine  or  bromine. 


65  THE   ALCOHOLS 

with  the  production  of  aldehyde,   and  then  replaces  hydrogen 
(cf.  p.  92). 

Isomeric  Alcohols. — It  is  evident  from  the  principles  of  isom- 
erism  which  we  have  studied,  that  beginning  with  propane, 
different  hydroxyl  derivatives  of  the  hydrocarbons,  or  different 
alcohols,  of  the  same  molecular  weight,  are  possible.  We  find 
here,  as  in  the  other  cases,  that  the  facts  agree  with  the  theory; 
there  are  two  propyl  alcohols, 

CH3.CH2.CH2OH  and  CH3.CHOH.CH3; 
four  butyl  alcohols, 

CH3.CH2.CH2.CH2OH, 

(CH3)2:CH.CH2OH,  CH3.CH2.CHOH.CH3,  and  (CH3)3iC.OH; 
etc. 

The  formulas  of  these  alcohols  are,  of  course,  arrived  at  by  the 
consideration  of  the  reactions  of  the  various  alcohols  and  by  the 
manner  in  which  they  can  be  formed;  and  it  will  be  noticed  that  the 
hydroxyl  appears  in  three  different  groups : 

-  CH2.OH,  =  CH.OH,  and  =  COH, 
and  that  these  are  all  the  varieties  possible. 

Ethyl  alcohol  and  all  those  which  on  oxidation  first  yield  alde- 
hydes and  then  acids  containing  the  same  number  of  carbon 
atoms  as  the  alcohol,  are,  in  consequence,  given  formulas  with  the 
group  —  CH2OH.  In  ethyl  alcohol  and  its  higher  homologues, 
this  group  is  united  to  an  alkyl  group;  in  methyl  alcohol  we  as- 
sume, by  analogy,  the  presence  of  the  same  alcohol  group,  here 
united  with  hydrogen.  This  difference  probably  explains  the 
readier  oxidation  of  methyl  alcohol.  Alcohols  which  give  ketones 
as  the  first  oxidation  product,  and  then,  on  further  oxidation 
break  down  into  acids  with  a  smaller  number  of  carbon  atoms, 
are  characterized  by  the  group  =  CH.OH;  and,  finally,  those  which 
are  converted  at  once  into  ketones  or  acids  of  a  less  number  of 
carbon  atoms  have  =  C  —  OH  as  their  characteristic  group.  The 
first  variety  of  alcohols,  containing  —  CH2.OH,  are  called  primary 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  66 

alcohols;  those  with  =  CH.OH,  united  with  two  alkyl  groups, 
secondary;  and  those  with  =  C  —  OH,  with  three  alkyl  groups, 
tertiary  alcohols. 

Some  of  the  experimental  evidence  for  the  assignment  of  these 
groups  will  be  given  in  Chapter  VIII.  Here  we  will  only  state  that 
the  primary  and  secondary  alcohols  can  be  formed  by  reduction 
(nascent  hydrogen)  of  aldehydes  and  ketones,  respectively. 

Methods  of  Formation. — The  principal  laboratory  methods  for 
forming  primary  alcohols  are: 

1.  Substitution  of  hydroxyl  for  a  halogen  atom  or  other  acid 
radical  in  alkyl  halides  or  other  esters  by  the  action  of  hydroxides 
of  the  metals  or  water  (for  the  halides,  moist  silver  oxide,  which 
acts  as  silver  hydroxide,  is  especially  good;  cf.  p.  34). 

2.  From  alkyl  amine  nitrites   (cf.  p.   131)   on  heating  their 
aqueous  solutions: 

CH3(NH2).HNO2  =  CH3OH  +  N2  +  H20 
This  reaction  is  analogous  to  that  of  ammonium  nitrite  when  heated. 

3.  By  reduction   (with  sodium  amalgam)   of  aldehydes    and 
ketones: 

CH3.CHO  +  2H  =  CH3.CH2OH 

Aldehyde  Ethyl  alcohol 

CH3.CO.CH3  +  2H  =  CH3.CHOH.CH3 

Acetone  Sec.  propyl  alcohol 

4.  The  Grignard  reactions  for  secondary  and  tertiary  alcohol. 
It  is  not  necessary  to  give  here  other  special  reactions  for  the 

formations  of  the  three  classes  of  alcohols.  Although  the  alcohols 
are  often  spoken  of  as  derivatives  of  the  hydrocarbons,  it  must 
not  be  forgotten  that  the  direct  substitution  of  OH  for  H  in  a 
hydrocarbon  is  always  impossible. 

In  some  discussions,  methyl  alcohol  is  called  "carbinol"  and 
the  other  primary  alcohols  are  considered  as  derivatives  of  it 
by  the  replacement  of  hydrogen  by  alkyl  groups:  thus  ethyl 
alcohol  is  methyl  carbinol;  secondary  butyl  alcohol,  CH3.CH2.- 
CHOH.CH3,  is  methyl-ethyl-carbinol,  etc. 

Fusel  oil,  which  is  formed  in  small  amounts  in  the  fermenta- 


67 


THE   ALCOHOLS 


tion  which  produces  ethyl  alcohol,  is  composed  chiefly  of  two  of 
the  eight  possible  amyl  alcohols: 

CH3v 
(CH3)2:  CH.CH2.CH2OH,  isoamyl  alcohol,  and        >CH.CH2OH, 


active  amyl  alcohol.  The  former  comprises  70-80  per  cent,  of  the 
fusel  oil.  The  latter  has  the  property  of  "optical  activity"  or 
power  of  rotating  the  plane  of  polarized  light  (cf.  p.  1  69)  .  Normal 
propyl  alcohol  and  isobutyl  alcohol  —  isopropylcarbinol  —  are  also 
found  in  fusel  oil.  Fusel  oil  has  a  characteristic  odor,  and  is  poi- 
sonous. It  distils  with  the  ethyl  alcohol,  though  having  a  much 
higher  boiling  point,  and  is,  therefore,  found  in  crude  spirituous 
liquors,  and  is  responsible  in  part  for  their  specially  disagreeable 
effects.  It  is  destroyed  more  or  less  completely  by  the  "aging" 
of  the  liquor. 

Fusel  oil  is  used  as  the  source  of  iso-amyl  alcohol  and  various 
esters  derived  from  it,  such  as  the  acetate  ("pear  oil"),  the  iso- 
valerate  ("apple  oil"),  and  the  nitrite,  which  find  a  number  of 
uses  Amyl  alcohol  itself  is  employed  occasionally  as  a  solvent 
for  alkaloids,  etc.  None  of  the  other  alcohols,  except  methyl 
and  ethyl  alcohols,  are  of  any  especial  practical  importance. 


NORMAL 

PRIMARY  ALCOHOLS 

Name 

Formula 

Melting  Point    Boiling  Point      Specific  Gravity 

Methyl 

CH3OH 

—97.8                  66.7°           0.812 

Ethyl 

C2H6OH 

—  117.6                      78.4                0.806 

Propyl 

C3H7OH 

97 

0.817 

> 

Butyl 

C4H9OH 

117 

0.823 

rt- 

Pentyl  (Amyl) 

C6HnOH 

138 

0.829^  Rg" 

Hexyl 

CeHiaOH 

I57 

0-833 

0°* 

Heptyl 

C7H16OH 

176 

0.836 

1 

Octyl 

C8H17OH 

195 

0.839 

Nonyl 

C9H19OH 

-5°                 213 

o.842J     ^ 

Decyl 

C10H21OH 

+  7                   231 

0.839 

IB 

Dodecyl 

C12H25OH 

24                  143 

^  >        0-831 

II 

Tetradecyl 

C14H29OH 

38                  167 

fl>M                     0.824 

Cetyl 

C18H33OH 

50                  190 

S3        0.818 

si 

Octadecyl 

Ct8H37OH 

59                  211 

P-3        0.813  J 

°l 

Myricyl 

CsoHdOH 

86 

0.808 

INTRODUCTION   TO    ORGANIC   CHEMISTRY  68 

It  will  be  noticed  that  the  boiling  points  of  these  alcohols  from 
ethyl  alcohol  to  decyl  alcohol  increase  with  approximate  regu- 
larity, the  average  increment  being  19°.  The  boiling  points  of 
the  last  four  are  not  comparable  with  those  of  the  first  ten  since 
they  are  determined  under  reduced  pressure,  but  when  compared 
with  each  other  it  is  seen  that  the  differences  are  less.  A  similar 
decrease  in  boiling-point  differences  is  observed  in  the  normal 
paraffins  (cf.  table  on  page  17)  and  in  other  homologous  series; 
and  in  general,  in  the  higher  members  of  a  series,  the  uniform 
increase  of  molecular  weight  by  the  addition  of  CH2  has  less  and 
less  effect  on  the  physical  properties  of  the  members.  The  dif- 
ference between  the  boiling  points  of  methyl  and  ethyl  alcohols 
is  12  instead  of  19,  and  the  specific  gravity  of  methyl  alcohol  is 
greater  than  that  of  ethyl  alcohol  instead  of  less  as  it  should  be 
to  conform  with  the  general  changes  in  specific  gravity  of  the 
other  members.  Such  irregularities  are  found  in  other  series, 
and  correspond  to  the  somewhat  different  chemical  behavior 
often  observed  in  the  derivatives  of  methane  as  compared  with 
their  homologous  compounds. 

The  effect  of  structure  on  the  boiling  point  is  shown  in  the 
following  table  of  the  amyl  alcohols. 

ISOMERIC  AMYL  ALCOHOLS 


Formula  Boiling  Point 

i.CH2.CH2.CH2OH  138' 

Primary         (CH3)2CH.CH2.CH2OH  _i  131 


Secondary 


f  CH3.CH2.CH2.CH2.CH2OH  138° 

CH3.CH(C2H5).CH2OH  128 

CH3.CH2.CH2.CHOH.CH3  up 

(CH3)2CH.CHOH.CH8  112.5 


CH3.CH2.CHOH.CH2.CH3  117 

Tertiary         (CH3)2COH.CH2.CH3  102 

Unsaturated  Alcohols 

These  are  hydroxyl  compounds  in  which  a  double  or  triple 
bond  between  two  carbon  atoms  occurs.     A  number  of  alcohols 


69  THE   ALCOHOLS 


of  the  general  formula  CnHan^OH  are  known,  but  the  first 
member  of  the  series,  Vinyl  alcohol,  CH2:CHOH,  has  not  been 
isolated  —  the  reactions  which  should  produce  it  resulting  in  the 
formation  of  acetaldyde,  CH3.CHO,  which  is  isomeric  with  it. 
No  simple  alcohol,  in  fact,  has  a  stable  existence  in  which  the 
carbon  atom  carrying  the  hydroxyl  group  is  combined  with  another 
carbon  atom  by  a  double  or  triple  bond.  The  first  and  best 
known  of  the  unsaturated  alcohols  is  allyl  alcohol,  CH2:  CH.CH2- 
OH.  It  occurs  in  small  amounts  in  crude  wood  alcohol,  and  can 
be  made,  mixed  with  other  products,  from  glycerol  and  oxalic 
acid.  The  reaction,  which  is  a  somewhat  complicated  one, 
will  be  discussed  under  formic  acid  (p.  105).  Allyl  alcohol  is  a 
colorless  liquid  of  very  sharp  odor,  which  boils  at  96.6°,  and  mixes 
with  water  in  all  proportions.  It  gives  reactions  which  are 
characteristic  of  a  primary  alcohol,  and  also  such  as  belong  to  an 
unsaturated  hydrocarbon. 

Propargyl  alcohol,  CH  =  C.CH2OH,  is  the  chief  representa- 
tion of  alcohols  with  a  triple  bond,  and  which  have  the  general 
formula,  CnH2n_3OH.  It  is  made  by  reactions  of  the  kind 
which  have  been  given  for  the  production  of  members  of 
the  acetylene  series  and  for  the  introduction  of  the  hydroxyl 
group.  It  is  a  liquid  boiling  at  1  15°  and  gives  reactions  in  accord- 
ance to  the  structure  which  is  attributed  to  it. 

Quite  a  number  of  alcohols  with  two  double  bonds  have'  beer 
made  in  the  laboratory  and  some  representations  of  this  grouf 
have  been  found  in  nature.  The  general  formula  of  these  alco 
hols  is  the  same  as  that  for  the  alcohols  with  a  triple  bond. 


CHAPTER  VI 
THE  ETHERS 

Ethyl  Ether. — Ordinary  ether  is  obtained  by  the  action  of  sul- 
phuric acid  on  alcohol,  and  is  often  called  "sulphuric  ether"  for 
that  reason,  though  it  contains  no  sulphur  or  sulphur-oxygen 
group.  Alcohol  and  concentrated  sulphuric  acid  are  mixed  in  the 
proportion  of  about  one  to  two,  so  that  distillation  begins  at  about 
140°,  and  then  alcohol  is  gradually  added  so  that  the  boiling 
point  is  kept  nearly  constant.  Some  sulphur  dioxide  from  the 
reduction  of  sulphuric  acid,  and  other  products  from  alcohol 
besides  ether  are  formed  at  the  same  time.  The  ether  formation, 
which,  theoretically,  should  continue  indefinitely,  comes  to  an 
end  when  alcohol  to  the  amount  of  about  four  times  the  weight 
of  the  sulphuric  acid  has  been  used.  It  will  be  recalled  that  a 
mixture  of  concentrated  sulphuric  acid  and  alcohol  is  used  for  the 
preparation  of  ethylene  (p.  46).  The  chief  product  is  seen  to 
depend  on  the  proportions  of  acid  and  alcohol  and  the  tempera- 
ture at  which  the  reaction  is  carried  on.  This  is  an  illustration 
of  the  greater  flexibility  of  organic  reactions  as  compared  with  the 
usual  inorganic  reactions. 

The  distillate  contains  water,  alcohol,  and  some  sulphur  dioxide, 
mixed  with  the  ether.  The  addition  of  sodium  carbonate  neu- 
tralizes and  fixes  the  sulphurous  acid,  and  renders  the  ether  less 
soluble.  The  ether  forms  a  layer  on  top  of  the  solution,  and,  after 
separation  from  the  aqueous  solution,  most  of  the  water  and  some 
of  the  alcohol  which  is  still  mixed  with  it  is  absorbed  by  calcium 
chloride  or  quicklime,  and  the  ether  is  distilled.  It  still  contains 
small  amounts  of  water  and  alcohol  which  may  be  removed  by 
shaking  it  with  shavings  of  bright  sodium,  and  again  distilling. 

70 


71  THE   ETHERS 

Properties. — Ether  is  a  colorless,  very  thin  liquid  of  the  well- 
known  characteristic  odor.  It  is  very  volatile,  giving  a  vapor 
which  is  two  and  a  half  times  heavier  than  air;  boils  at  34.6°  and 
has  a  specific  gravity  of  0.718  at  15.6°.  It  dissolves  in  about 
eleven  times  its  volume  of  water  at  25°,  and  in  turn  dissolves 
about  2  per  cent,  of  its  volume  of  water.  It  and  its  vapor  are 
very  easily  inflammable  and  all  operations  with  it  must  be  con- 
ducted with  great  care  to  avoid  its  ignition.  Chemically,  it  is 
a  neutral  substance  and  rather  inert.  Unlike  alcohol,  it  is  not 
acted  on  by  sodium  or  potassium,  nor  by  phosphorus  chlorides 
in  the  cold.  When  heated  with  phosphorus  pentachloride, 
ethyl  chloride  is  formed. 

Formula. — The  molecular  formula  of  ether  derived  from  its 
analysis  and  vapor  density  is  C4HioO.  The  formation  of  ethyl- 
ene  from  alcohol  was  explained  by  the  abstraction  of  the  ele- 
ments of  one  molecule  of  water  from  one  molecule  of  alcohol. 
The  ether  reaction  goes  on  at  a  lower  temperature,  and  is  hence 
presumably  less  drastic.  The  withdrawal  of  a  molecule  of  water 
would  presumably  take  place  more  readily  from  two  molecules 
of  alcohol  than  from  one,  and  this  would  give  us  the  formula  of 
ether: 

2C2H5OH  -  H2O  =  C4H10O 

Knowing  that  alcohol  is  the  hydroxide  of  ethyl,  the  probable 
structure  of  ether  is,  therefore,  (€2115)20,  or  ethyl  oxide.  That 
it  does  not  contain  a  hydroxyl  group  is  shown  by  the  failure  of 
sodium  to  act  on  it. 

The  reaction  is  not,  however,  quite  as  simple  as  indicated  by 
the  above  equation.  Ethyl  sulphuric  acid  is  first  formed  and 
then  reacts  with  a  second  molecule  of  alcohol: 

C2H5OH  +  H2SO4  =  C2H5.HSO4  +  H2O 
C2H5.HSO4+  C2H5OH  =  (C2H6)20  +  H2SO4 

The  constitution  given  to  the  ether  molecule  is  confirmed 
by  the  other  methods  of  its  formation  and  by  all  of  its  chemical 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  72 

behavior.  Thus,  ether  is  formed  when  ethyl  bromide  or  iodide 
reacts  with  certain  oxides.  The  iodide  and  dry  silver  oxide  react 
at  once  with  evolution  of  heat: 

2C2H5I  +  Ag20  =  (C2H5)20  +  2AgI 

A  similar  reaction  with  sodium  oxide  takes  place  at  180°, 
and  ether  is  formed  even  when  the  iodide  is  sufficiently  heated  with 
a  small  amount  of  water.  The  temperature  required  for  these 
last  two  reactions  makes  it  necessary  to  carry  them  out  in  sealed 
tubes.  Attention  has  been  called  to  the  fact  that  the  reaction 
between  alcohols  and  acids  with  the  formation  of  esters  and  water 
is  a  reversible  reaction.  Now,  when  ethyl  iodide  (an  ester)  and 
water  react,  the  first  products  are  alcohol  and  hydrogen  iodide: 

C2H5I  +  H2O  *±  C2H5OH  +  HI 

and  under  proper  conditions  the  alcohol  and  the  still  unchanged 
ethyl  iodide  form  ether  and  hydrogen  iodide: 

C2H5OH  +  C2H5I  ±?  (C2H5)20  +  HI 

An  excess  of  water  would  transform  almost  all  of  the  iodide  into 
alcohol,  so  only  a  small  amount  must  be  used  if  ether  is  to  be 
produced. 

Ether  is  also  formed  when  sodium  ethoxide  and  ethyl  iodide 
are  brought  together  in  alcoholic  solution: 

C2H5ONa  +  C2H5I  =  (C2H5)20  +  Nal 

This  synthesis  of  ether  is  of  great  historical  importance,  as  it 
not  only  served  to  establish  the  structure  of  ether,  but  also  had 
a  far-reaching  effect  in  clearing  up  the  structural  formulas  of 
many  other  compounds.  It  was  made  by  Williamson  in  1850. 
The  student  should  read  his  papers  on  etherification  in  the 
Alembic  Club  Reports,  No.  16. 

Reactions.  — All  the  reactions  of  ether  are  in  accordance  with 
this  view  of  its  molecular  structure.  The  production  of  ethyl 


73  THE   ETHERS 

chloride  when  ether  is  heated  with  phosphorus  pentachloride 
shows  that  two  chlorine  atoms  have  replaced  the  one  oxygen 
atom  which  unites  two  ethyl  groups: 

C2H6C1 


2.  Ethyl  halides  are  formed  when  the  halogen  acids  react  with 
ether,  hydrogen  iodide  acting  more  readily  than  the  others.     At 
o°  hydrogen  iodide  produces  ethyl  iodide  and  ethyl  alcohol: 

(C2H5)20  +  HI  =  C2H6I  +  C2H6OH 

but  when  heated  with  the  strong  acid  the  products  are  ethyl 
iodide  and  water: 

(C2H5)2O  +  2HI  =  2C2H5I  +  H2O 

3.  Ether  dissolves  in  cold  concentrated  sulphuric  acid  and  can 
be  separated  unchanged  from  the  solution  by  pouring  the  acid 
solution  into  water.     When  the  solution  of  ether  in  the  acid  is 
warmed,  however,  ethyl  sulphuric  acid  is  formed: 

(C2H5)2O  +  2H2SO4  =  2(C2H5)HSO4  +  H2O 

4.  When  heated  with  water  containing  a  little  sulphuric  acid 
to  150-180°  ether  is  hydrolyzed  into  alcohol: 

(C2H5)2O  +  H2O  =  2C2H5OH 

5.  Oxidation  by  means  of  nitric  or  chromic  acid  produces  the 
same  products  as  those  obtained  by  the  oxidation  of  alcohol  — 
aldehyde  and  acetic  acid: 

(C2H5)2O  +  20  =  2CH3.CHO  +  H2O 
(C2H6)2O  -f  40  =  2CH3.CO.OH  +  H2O 

6.  Chlorine  replaces  the  hydrogen  step  by  step,  with  the  final 
formation  of  (C2C15)2O,  a  solid  compound  melting  at  69°  and 
having  a  penetrating  camphor-like  odor. 

Uses.  —  Besides  its  use  as  a  valuable  anaesthetic,  ether  is  much 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  74 

employed  in  the  laboratory  and  in  the  arts  and  manufactures 
as  an  excellent  solvent  for  many  substances.  These  are  readily 
recovered  from  their  solutions  in  it,  on  account  of  its  great  vola- 
tility and  low  boiling  point.  Thus  it  is  used  for  the  extraction 
of  fats,  oils,  etc.,  from  mixtures.  It  not  only  dissolves  many 
organic  compounds,  but  also  a  number  of  inorganic  substances, 
such  as  iodine,  chromic  acid,  and  chlorides  of  iron,  mercury, 
and  tin.  In  its  rapid  change  into  vapor,  ether  produces  such  a 
lowering  of  temperature  that  it  has  been  used  to  manufacture 
ice;  and  in  the  form  of  a  fine  spray  on  the  skin  to  produce  local 
anaesthesia. 

Other  Ethers. — By  methods  similar  to  those  which  produce 
ethyl  ether,  many  other  ethers  can  be  made  whose  reactions  are 
like  those  of  this  ether  and  whose  properties  have  the  relation- 
ship and  show  the  gradation  which  are  familiar  to  us  in  com- 
pounds forming  a  homologous  series.  The  general  formula  of 
an  ether  is  CnH2n+2O,  in  which,  however,  n  cannot  be  less 
than  two.  For  if  n  =  o,  we  have  H2O,  and  if  n  =  i,  CH4O  or  methyl 
alcohol.  Both  of  these  substances  may  be  considered  of  the 
ether  type,  since  ether,  water,  and  methyl  alcohol  are  all  oxides. 
But  an  ether  is  an  alkyl  oxide,  while  water  is  hydrogen  oxide,  and 
methyl  alcohol,  methyl-hydrogen  oxide.  The  first  ether,  then, 
is  methyl  ether  (CH3)2O. 

Methyl  and  ethyl  ether  each  contain  two  like  alkyl  groups. 
But  from  the  methods  of  ether  formation  we  should  expect  it 
possible  to  make  ethers  containing  two  dissimilar  groups,  and  this 
can,  in  fact,  be  readily  done.  When  a  mixture  of  two  alcohols 
is  treated  with  sulphuric*  acid,  as  in  the  preparation  of  ethyl 
ether,  a  mixture  of  ethers  results:  from  methyl  and  ethyl  alcohols 
there  is  formed  methyl  ether,  (CH3)20;  ethyl  ether,  (C2H5)2O; 
and  methyl-ethyl  ether,  CH3.O.C2H5.  A  definite  single  mixed 
ether  is  obtained  by  the  reaction  of  a  sodium  alkoxide  and  an 
alkyl  iodide: 

CH3ONa  +  C2H5I  =  CH3.O.C2H5+NaI 


75  THE   ETHERS 

This  formation  of  a  mixture  of  ethers  and  of  single  mixed  ethers 
was  used  by  Williamson  to  confirm  his  theory  of  the  structure  of 
ether  and  alcohol. 

The  ethers  with  two  like  alkyl  groups  are  called  simple  ethers, 
the  others  mixed  ethers.  The  first  two  ethers  which  correspond  to 
the  general  formula,  namely,  (CHa^O  and  CH3.O.C2H5,  are  gases 
at  ordinary  temperature.  All  the  other  ethers,  except  those  of 
high  molecular  weights,  are  liquids,  lighter  than  water. 

A  few  unsaturated  ethers  are  known,  e.g.,  divinyl  ether  (CHa : 
CH)2O,  and  ethyl-propargyl  ether,  CH:.C.CH2.O.C2H5. 

ETHERS 

Boiling  Specific 

Names  Formulas  Points  Gravity 

Dimethyl  Ether  (CH3)2O  -23.6° 

Diethyl  (C2H6)2O  34-6  0.731    (4°) 

Dipropyl  (C3H7)2O  90.7  0.763    (o°) 

Dibutyl  (normal)  (C4H9)2O  141  0.784    (o°) 

Dioctyi  (normal)  (C8Hi7)2O  280-282  0.805  (17°) 

Methyl-ethyl  CH3OC2H6  n                    

Ethyl-propyl  C2H6OC3H7  63-64  0.739(20°) 

Ethyl-butyl  (norm.)  C2H5OC4H9  92  0.769    (o°) 

Ethyl-octyl  (norm.)  CsHsOCgHn  182-184  0.794(17°) 


CHAPTER  VII 

OXIDATION  PRODUCTS  OF  ALCOHOLS 
ALDEHYDES  AND  KETONES 

Aldehydes 

Ethyl  alcohol  reacts  readily  with  a  dilute  solution  of  chromic 
acid  (potassium  dichromate  and  sulphuric  acid).  Heat  is  devel- 
oped and  the  first  portions  of  the  distillate  contain  a  substance 
called  aldehyde,  which  has  a  peculiar  and  suffocating  odor. 
When  separated  from  the  water,  alcohol,  and  small  amounts  of 
other  substances  with  which  it  is  mixed,  the  pure  aldehyde  is 
obtained  as  a  liquid  which  boils  at  21°.  Its  analysis  and  vapor 
density  lead  to  the  molecular  formula,  C2H4O.  The  oxidation 
of  alcohol  to  aldehyde  consists,  therefore,  in  the  removal  of  two 
hydrogen  atoms  from  the  alcohol  molecule  C2H6O,  and  it  is  from 
this  fact  that  the  name  aldehyde — alcohol  dehydrogena.tus — was 
given  it: 

CH3.CH2.OH  +  O  =  C2H40  +  H2O 

There  are  three  possible  arrangements  of  the  atoms  in  this 
formula: 

CH3  CH2 

2, 


=O  C— O— H     and  >O 

I  I  CH/ 

H  H 

Two  reactions  will  help  us  to  decide  which  of  these  arrange- 
ments properly  represents  the  structure  of  the  alehyde  molecule, 
i.  Phosphorus  pentachloride  acts  on  aldehyde  with  the  pro- 


77  ALDEHYDES   AND   KETONES 

duction  of  a  compound  whose  formula  is  C2H4Cl2,  and  whose 
structure  must  be  CH2C1.CH2C1  or  CH3CHC12.  This  cuts  out 
the  second  of  the  possible  aldehyde  formulas,  which  contains  a 
hydroxyl  group,  and  from  which  we  should  consequently  expect 
phosphorus  pentachloride  to  produce  CH2  :  CHC1. 

2.  Aldehyde  is  readily  oxidized  to  a  monobasic  acid,  C2H4O2, 
three  of  whose  hydrogen  atoms  only  can  be  replaced  by  chlorine 
by  the  direct  action  of  this  halogen,  giving  C2ClsHO2,  which  is 
still  a  monobasic  acid.  We  may  conclude,  therefore,  that 
in  the  acid,  and  in  the  aldehyde  from  which  it  is  made,  there 
is  a  CH3  group.  The  structural  formula  of  the  aldehyde  ap- 
pears, therefore,  to  be  the  first  one  of  the  three, 


All  the  reactions  by  which  aldehyde  is  formed,  and  all  of  the 
reactions  it  gives,  afe  in  accord  with  this  view  of  its  structure. 
Acetaldehyde,  CH3.CHO,  is  usually  prepared  by  oxidizing 
alcohol  in  the  way  stated  above.  It  is  also  produced  when  a 
mixture  of  calcium  acetate  and  calcium  formate  is  heated: 


CH3 

=   |         +  CaCO3 
HCOaca1  CHO 

Acetaldehyde  can  also  be  formed  from  ethylidene  chloride  or 
bromide  (p.  40)  by  heating  with  water  in  sealed  tubes,  or  by  boil- 
ing with  alkalies: 

CH3CHBr2  +  H2O  =  CH3CHO  +  2HBr 

This  reaction  is  of  interest,  but  of  no  practical  importance  as  a 
method  of  preparation,  since  these  halides  themselves  are  usually 
made  from  aldehyde  by  phosphorus  halides. 

Another  method  of  formation  of  theoretical  interest  is  from 
unsaturated  hydrocarbons  of  the  acetylene  series,  by  the  addition 
of  the  elements  of  water.  This  occurs  when  the  hydrocarbon  is 

1  For  the  sake  of  greater  simplicity  in  the  equation,  ca  =  \  Ca. 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  78 

dissolved  in  strong  sulphuric  acid  which  is  then  largely  diluted 
and  distilled: 

CH  :  CH  +  H2O  =  CH3CHO 

Properties  and  Reactions. — Acetaldehyde  is  a  very  volatile 
liquid  which  boils  at  21°,  and  mixes  with  water  in  all  proportions. 
It  dissolves  sulphur,  phosphorus  and  iodine.  It  is  easily  inflam- 
mable and  burns  with  a  bright  flame. 

1.  It  is  very  readily  oxidized  to  acetic  acid,  even  in  dilute 
solutions,  and  this  change  goes  on  slowly  when  it  is  in  contact 
with  air.    Hence  it  is  a  powerful  reducing  agent.     When  warmed 
with  an  alkaline  solution  of  copper  sulphate  (Fehling's  Solution) 
it  precipitates  red  cuprous  oxide.     Even  very  dilute  solutions 
(1:4000)  reduce   ammoniacal  solutions  of  silver  nitrate,  sepa- 
rating the  silver  in  a  finely  divided  state  and  giving  to  the  solu- 
tion a  violet  color.     Stronger  solutions  precipitate  most  or  all  of 
the  silver  as  a  mirror  on  the  walls  of  the  vessel. 

2.  When    sodium  amalgam  is  put  into  its  aqueous  solution, 
aldehyde  is  "reduced"   to  alcohol  by  the  direct  addition  of 
hydrogen: 

CH3.CHO  +  2H  =  CH3.CH2.OH 

3.  A  number  of  other  addition  products  are  formed  with  various 
substances,  in  which,  as  in  this  instance,  the  double  bond  which 
unites  oxygen  to  carbon  in  the  CHO  group  is  changed  to  a  single 
bond  so  that  the  oxygen  becomes  a  linking  atom.     Such  reac- 
tions occur  with  ammonia,  acid  sodium  sulphite,  and  hydrocyanic 
acid: 

/OH 
CH3.CHO  +  NH3         =  CH3.CH< 

XNH2 
/OH 
CH3.CHO  +  NaHSO3  =  CH3.CH< 

XS03Na 

/OH 
CH3.CHO  +  HCN       =    CH3CH< 

X 


79  ALDEHYDES   AND   KETONES 

The  ammonia  addition  product  is  precipitated  in  crystals 
when  dry  ammonia  gas  is  led  into  a  cold  solution  of  aldehyde  in 
anhydrous  ether.  It  is  very  soluble  in  water.  In  air  it  slowly 
decomposes  into  resinous  substances. 

The  sodium  sulphite  compound  is  also  a  solid  crystalline  sub- 
stance which  is  obtained  by  shaking  aldehyde  with  a  saturated 
solution  of  the  sulphite. 

Aldehyde  is  recovered  from  both  of  these  compounds  when  they 
are  heated  with  dilute  acids,  and  on  this  account  they  are  some- 
times made  as  a  means  of  isolating  and  purifying  aldehyde. 

The  hydrocyanic  compound  is  the  nitrile  of  lactic  acid  (p.  165), 
into  which  it  is  converted  by  hydrolysis. 

4.  With  anhydrides  of  organic  acids  (cf.  p.  117)  addition  prod- 
ucts are  also  formed: 

CH3.CHO  +  (CH3.CO)20  =  CH3.CH(CH3.CO.O)2 

These  compounds  are  decomposed  by  water  into  aldehyde  and 
.acid,  or  more  readily  by  an  alkali  into  aldehyde  and  a  salt  of  the 
acid. 

5.  Another  reaction  which  is  common  to  the  aldehydes  is  one 
in  which  they  react  with  hydroxyl  compounds  with  elimination 
of  water.     Thus,  with  alcohol,  an  acetal  is  formed: 

CH3.CHO  +  2C2H5OH  *±  CH3.CH(OC2H5)2  +  H2O 

Diethylacetal 

The  reaction  is  aided  by  the  presence  of  a  little  acetic  acid  as  a 
catalyser.  It  is  reversed  when  the  acetals  are  boiled  with  acids 
and  water. 

6.  With  hydroxylamine  (p.  122)  aldehydes  react  to  form  ald- 
oximes: 

/H 
CH3.CHO  +  NH2OH  =  CHa.C^  +  H2O 


Acetoxime 


INTRODUCTION   TO    ORGANIC    CHEMISTRY  80 

Similar  products  from  ketones  are  called  ketoximes. 

Oximes  from  the  lower  members  of  the  aldehyde  and  ketone 
series  are  liquids  that  can  be  distilled  without  decomposition. 
The  hydrogen  of  their  hydroxyl  groups  can  be  replaced  by  alkali 
metals,  and  with  acids  they  form  addition  compounds  such  as, 
CH3.CH:N(OH)HC1.  On  heating  with  acids  they  are  hydro- 
lyzed  into  hydroxylamine  and  the  corresponding  aldehyde  or 
ketone.  Energetic  reduction  (sodium  amalgam  in  weak  acid 
solution)  converts  them  into  primary  amines. 

7.  A  somewhat  similar  reaction  occurs  with  hydrazine  and 
hydrazine  derivatives,  with  the  formation  of  hydrazones: 


CH3.CHO  +  H2N  -  NH2  =  CH3.<X  +  H2O 

Hydrazine  N NH9 

Hydrazone 

/H 

CH3.CHO  +  H2N  -  NH(C6H5)  =  CHg.CC 

Phenylhydrazine  ^N-NH(C6H5)  +  H2O 

Phenylhydrazone 

The  hydrazones  are  hydrolyzed  (the  above  reactions  reversed) 
by  boiling  with  dilute  acids.  The  ready  formation  of  oximes  and 
hydrazones  is  so  characteristic  of  compounds  containing  the 
carbonyl  group,  =C  =  O,  that  it  serves  as  an  excellent  means  for 
the  identification  of  this  group;  and  phenyl  hydrazones  have 
played  an  important  part  in  the  successful  investigation  of  sugars 
(cf.  p.  208). 

8.  With    chlorine,    aldehyde    forms,    in    dilute  solution,  tri- 
chloraldehyde  ("chloral"  p.  91),  but  in  strong  solutions  unless 
the  hydrochloric  acid  which  is  formed  is  neutralized,  this  causes 
the  production  of  "condensation"  products  such  as 

CH3.CHC1.CC12.CHO. 

9.  Phosphorus  halides,  as  has  been  already  stated,  replace  the 
oxygen  of  aldehyde  by  two  atoms  of  halogen: 

CH3.CHO  +  PC16  =  CH3.CHC12  +  POC13 


8l  ALDEHYDES  AND  KETONES 

10.  By  the  Grignard  reaction  aldehydes  may  be  converted  into 
secondary  alcohols.  Formaldehyde,  however,  yields  primary 
alcohols  (p.  37). 

Polymerization,  (a)  The  addition  of  a  few  drops  of  concen- 
trated sulphuric  acid  to  acetaldehyde  causes  it  to  become  hot 
and  boil  violently.  But  instead  of  being  all  volatilized,  the  ret- 
sult  is  a  colorless  liquid  which  boils  at  1 24°,  and,  when  solidified  by 
cold,  melts  at  10.5°.  It  is  soluble  in  about  eight  parts  of  water. 
It  shows  none  of  the  reactions  characteristic  of  aldehyde,  except 
the  reaction  with  phosphorus  halides.  When  boiled  with  dilute 
acids,  it  is  converted  into  aldehyde  again.  Its  empirical  formula 
is  the  same  as  that  of  aldehyde,  but  its  vapor  density  is  three 
times  as  great,  so  that  the  molecular  formula  is  CeH^Oa.  This 
polymer  of  aldehyde  is  called  paraldehyde.  The  fact  that 
paraldehyde  does  not  give  aldehyde  reactions  shows  that  it 
does  not  contain  the  aldehyde  group;  and  since  it  does  not  react 
with  sodium,  it  has  no  hydroxyl  group.  A  direct  linkage  of  the 
three  aldehyde  molecules  by  carbon  atoms  is  improbable,  while 
all  the  additive  reactions  we  have  studied  indicate  that  the 
oxygen  in  the  aldehyde  molecule  readily  shifts  one  of  its  double 
bonds  to  become  a  linking  atom.  Hence  the  formula  which 
is  given  to  paraldehyde  is, 

O-CH.CH3 

/        I 
CH3.CH        O 

\        I 
O-CH.CHs 

(b)  At  o°  a  little  hydrogen  chloride,  sulphur  dioxide,  or  dilute 
sulphuric  acid  causes  a  crystallization  to  take  place  in  aldehyde. 
Only  part  of  the  aldehyde  is,  however,  transformed.  This 
solid  substance  is  insoluble  in  water,  and  when  quickly  heated  it 
sublimes  without  melting,  at  about  112°,  being  partly  reconverted 
at  the  same  time  into  aldehyde.  By  continued  slower  heating  or 
by  distillation  with  a  little  dilute  sulphuric  acid,  the  conversion 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  82 

can  be  made  complete.  This  substance  is  called  metaldehyde. 
It  is  found  to  have  the  same  molecular  formula  as  paraldehyde, 
and  is  believed  to  be  a  "  stereo-isomer  "  of  it  (cf.  p.  166).  Like  the 
paraldehyde  it  gives  ethylidene  halides  with  phosphorus  penta- 
halide. 

(c)  Acetaldehyde  and  other  aldehydes,   with   the  exception 
of  formaldehyde,  are  converted  into  yellowish-brown  resinous 
substances  when  warmed  with  alkalies.     These  aldehyde-resins 
are  polymers  of  the  aldehydes,  but  of  unknown  structure. 

(d)  Aldol.  —  When  aldehyde  is  treated  with  a  dilute  solution 
of  alkali  or  with  certain  salts  (sodium  acetate,  zinc  chloride)  it 
is  changed  into  a  liquid  called  aldol,  which  has  twice  the  molecu- 
lar weight  of  aldehyde.     Unlike  the  other  polymers  of  aldehyde, 
aldol  gives  the  aldehyde  reactions,  and  it  cannot  be  converted 
back  into  aldehyde.     It  also  polymerizes  readily.     On  oxidation 
it  gives  a  hydroxy-butyric  acid,  CH3.CH.OH.CH2.CO.OH  (cf. 
p.  163),  which  has  a  chain  of  four  carbon  atoms.     It  appears, 
therefore,  that  aldol  is  an  addition  product  of  aldehyde  to  alde- 
hyde of  the  type  of  the  other  addition  products  such  as 

H 


and  in  which  a  carbon  atom  of  each  of  the  two  molecules  is 
united. 
The  formula  would  then  be, 

/H 
CH3.C^OH 

\CH2.CHO 

According  to  this  formula  aldol  would  be  an  alcohol  as  well 
as  an  aldehyde,  and  this  is  found  to  be  the  case.  The  name  aldol 
is  based  on  this  view,  aldehyde-alcohol.  When  heated,  aldol 
loses  the  elements  of  water  and  becomes  cro  tonic  aldehyde: 
CH3.CH:CH.CHO. 


83  ALDEHYDES   AND   KETONES 

Other  aldehydes  undergo  similar  "aldol  condensation,"  giving 
products  which  are  useful  in  many  organic  syntheses. 

The  Aldehyde  Series.  —  Acetaldehyde  is  a  typical  member  of  a 
series  of  saturated  aldehydes,  all  of  which  contain  the  character- 


istic  aldehyde  group  —  O\      ,  and  have  the  general  formula, 

H 

CnH2n+ICHO,  where  n  is  any  number  or  zero.  All  of  them, 
except  the  first  member,  are  formed  by  the  same  methods,  and 
give  the  same  reactions  as  acetaldehyde.  On  account  of  the 
readiness  with  which  they  react,  and  the  variety  of  products  that 
can  be  obtained  from  them,  aldehydes  are  much  employed  in 
synthetic  chemistry. 

The  first  member  of  the  series,  formaldehyde,  HCHO,  differs 
from  the  other  aldehydes  in  certain  ways,  which  can  be  attributed 
to  the  fact  that  it  alone  contains  no  alkyl  group,  but  only  hydrogen 
united  to  the  aldehyde  group. 

Nomenclature.  —  Aldehydes  are  usually  named  from  the  acids 
which  they  give  on  oxidation;  thus,  formaldehyde  from  formic 
acid,  acetaldehyde  from  acetic  acid,  and  propionic  and  butyric 
aldehydes  from  the  acids  of  these  names,  etc.  They  are  also 
named  from  the  corresponding  hydrocarbon  by  using  the  suffix 
al,  thus  methanal,  ethanal,  etc. 

Formaldehyde,  HCHO.  —  Methyl  alcohol  is  so  easily  oxidized 
that  the  method  used  for  the  preparation  of  acetaldehyde  is  not 
a  practical  one  for  making  formaldehyde.  But  when  a  mixture 
of  methyl  alcohol  vapor  and  air  are  brought  in  contact  with  heated 
platinum  or  copper  in  the  form  of  gauze  or  a  spiral  of  fine  wire,  a 
flameless  oxidation  occurs  with  the  formation  of  the  aldehyde. 
Once  started,  the  heat  of  the  reaction  is  sufficient  to  maintain  the 
temperature  of  the  contact  agent.  By  regulating  the  proportion 
of  air  and  passing  the  products  of  oxidation  through  a  condenser 
into  water,  a  30—40  per  cent,  solution  of  formaldehyde  with 
some  methyl  alcohol  may  be  obtained.  This  solution  is  sold 


INTRODUCTION   TO    ORGANIC    CHEMISTRY  g4 

under  the  name  of  "formalin."  Formaldehyde  is  a  gas  (boiling 
point—  21°),  of  very  penetrating  odor,  and  extremely  irritating 
to  the  eyes.  It  is  a  powerful  germicide,  and  is  much  used  for 
disinfecting  purposes,  both  as  gas  and  in  solution.  Its  solution 
is  also  used  in  small  amounts  as  a  food  preservative,  and  as  a 
preservative  for  anatomical  preparations.  Formaldehyde  hard- 
ens albuminous  substances  and  is  hence  used  in  histological 
work,  and  for  rendering  the  gelatine  films  of  photography  hard 
and  insoluble. 

According  to  the  general  reaction  for  the  formation  of  aldehydes 
by  heating  calcium  salts  with  a  formate,  formaldehyde  should  be 
produced  by  heating  calcium  formate:  ^ 

H.CO.Oca 


But  only  a  very  small  part  of  the  theoretical  amount  can  be  ob- 
tained in  this  way,  since,  at  the  temperature  necessary  for  the  reac- 
tion, the  aldehyde  breaks  up  into  carbon  monoxide  and  hydrogen. 
For  the  same  reason,  its  formation  from  methylene  halide,  CH2Cl2, 
and  water,  does  not  succeed. 

Reactions.  —  Formaldehyde  gives  most  of  the  reactions  of  the 
other  aldehydes,  but  differs  from  them  in  the  following  ways: 

It  is  oxidized  more  readily,  and  is  therefore  a  more  powerful 
reducing  agent;  not  only  reducing  silver  from  the  nitrate,  but 
also  forming  mercurous  choride  and  then  mercury  from  mercuric 
chloride  solutions.  While  its  other  addition  products  are  similar 
to  those  of  the  other  aldehydes,  it  reacts  with  ammonia  to 
form  hexamethylene  tetramine,  (CH2)6N4,  a  weakly  basic  sub- 
stance (p.  133).  Formaldehyde  in  solution  with  sodium 
hydroxide  gives  sodium  formate  and  methyl  alcohol: 

2HCHO  +  NaOH  =  HCO.ONa  +  CH3OH 
while  other  aldehydes  with  sodium  hydroxide  give  aldols  and 
resins.     If  hydrogen  peroxide  is  added  to  an  alkaline  solution, 
formaldehyde  is  oxidized  quantitatively  to  the  alkali  formate. 


85  ALDEHYDES   AND   KETONES 

This  is  made  the  basis  for  determining  the  amount  of  formalde- 
hyde in  solution.  A  standard  solution  of  sodium  hydroxide  is 
added  in  excess  and  then  hydrogen  peroxide.  The  alkali  remain- 
ing after  the  reaction  is  then  determined  by  titration  with  a 
standard  acid,  and  from  the  result  the  amount  of  the  formalde- 
hyde is  calculated.  The  reaction  is: 

HCHO  +  NaOH  +  H2O2  =  HCO.ONa  +  2H2O 
Formaldehyde  with  Grignard's  reagents  gives  primary  alcohols 

(P.  37). 

Polymerization. — Formaldehyde  polymerizes  very  readily  when 
its  solution  is  evaporated  over  sulphuric  acid  or  by  heat,  and  often 
on  standing  exposed  to  the  air.  Part  of  the  aldehyde  is  given  off 
as  gas,  but  the  greater  part  remains  as  a  white  solid,  which  can 
be  sublimed,  and  after  sublimation  melts  at  171°- 17 2°.  This 
is  called  metaformaldehyde,  (HCHO)X,  of  unknown  molecular 
weight.  It  is  only  slightly  soluble  in  ether  and  alcohol.  In  con- 
tact with  water  it  slowly  goes  into  solution,  and  this,  when 
diluted,  shows  by  the  freezing-point  method  that  the  aldehyde  is 
now  in  the  monomolecular  condition.  The  density  of  the  vapor 
of  metaformaldehyde  corresponds  to  the  simple  formula,  HCHO, 
but  on  cooling,  it  gradually  polymerizes  again.  Metaformalde- 
hyde is  sold  in  the  form  of  tablets  and  candles  under  the  name  of 
"paraform,"  and  these  are  used  as  a  source  of  formaldehyde  for 
disinfecting  purposes. 

In  the  presence  of  dilute  alkalies,  formaldehyde  polymerizes  to 
substances  from  which  it  cannot  be  readily  regenerated.  From 
a  solution  saturated  with  calcium  hydroxide  and  frequently 
shaken  till  the  smell  of  the  aldehyde  has  disappeared,  a  mixture 
of  sweet,  sugar-like  substances  is  obtained  from  which  Fischer 
isolated  a  substance  called  acrose  which  closely  resembles  natural 
sugars  and  has  the  same  empirical  formula  as  grape-sugar. 

This  laboratory  synthesis  of  a  sugar  from  formaldehyde  is  of 
especial  interest  in  connection  with  the-  natural  production  of 
sugars  and  other  carbohydrates  in  plants.  Under  the  influence 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  86 

of  sunlight  and  the  chlorophyll  of  the  leaves,  it  seems  probable 
that  the  first  product  of  the  reduction  of  the  carbon  dioxide  is 
formaldehyde:  CO2  +  H2O  =  HCHO  +  O2,  and  that  this  imme- 
diately polymerizes:  6HCHO  =  C6Hi2O6. 

Tests  for  Aldehydes. — The  formation  of  a  silver  mirror  or 
reduction  of  Fehling's  solution  together  with  the  production  of  a 
resin  on  heating  with  a  strong  alkali  indicate  the  probable  presence 
of  an  aldehyde.  The  colorless  solution  formed  by  adding  sul- 
phurous acid  to  rosaniline  (Schiff's  reagent)  is  turned  red-violet 
when  an  aldehyde  is  brought  into  it.  Since  formaldehyde  is 
often  used  as  a  food  preservative  a  simple  test  for  its  detection 
is  of  interest.  Milk,  for  instance,  may  be  tested  for  formaldehyde 
as  follows:  The  milk  is  diluted  with  an  equal  amount  of  water 
and  a  few  drops  of  a  solution  of  ferric  chloride  are  added.  Con- 
centrated sulphuric  acid  is  now  poured  slowly  into  the  inclined 
test  tube  so  that  it  goes  to  the  bottom  as  in  the  well-known  test 
for  nitric  acid.  If  formaldehyde  is  present  a  violet  ring  appears 
where  the  two  layers  of  liquid  are  in  contact,  when  the  tube  is 
put  into  hot  water.  The  color  is  the  result  of  a  reaction  between 
a  product  formed  in  milk  by  the  aldehyde  and  the  reagents  which 
are  added,  and  any  solution  may  be  tested  for  formaldehyde  in 
this  way  if  milk  is  first  added  to  it.  The  test  is  a  very  delicate 
one,  showing  the  presence  of  the  aldehyde  in  200,000  parts  of 
solution. 

Unsaturated  aldehydes  may  be  formed  by  oxidation  of  un- 
saturated  primary  alcohols,  or  from  saturated  aldehydes  by 
methods  for  producing  the  unsaturated  condition  (cf.  p.  45). 
Some  of  the  unsaturated  aldehydes  occur  in  "essential  oils." 

Acrylic  aldehyde,  acrolein,  CH2:  CH.CHO,  is  the  first  of  the 
possible  aldehydes  with  a  double  bond.  It  is  formed  by  the  oxi- 
dation of  allyl  alcohol  (p.  69),  but  is  made  more  readily  by  the 
withdrawal  of  the  elements  of  water  from  glycerol  (p.  159),  as 
by  heating  it  with  potassium  hydrogen  sulphate: 

CH2OH.CHOH.CH2OH  -  2H2O  =  CH2:  CH.CHO 

Glycerol  Acroleln 


87  ALDEHYDES   AND   KETONES 

Acrylic  aldehyde  is  a  liquid  boiling  at  52.4°.  It  has  a  penetrating 
odor  which  brings  tears  to  the  eyes.  Small  amounts  of  it  are 
formed  when  fats  and  oils  (which  are  glyceryl  esters)  are  heated, 
and  it  is  partly  responsible  for  the  odor  they  give.  Acrylic 
aldehyde  gives  all  the  reactions  of  an  aldehyde  and  of  an  unsatu- 
rated  hydrocarbon,  with  some  modifications.  For  instance  ,  with 
ammonia  it  reacts  to  form  C6H9NO,  a  glue-like  substance,  and 
H2O,  instead  of  the  usual  addition  product  of  an  aldehyde;  and 
it  combines  additively  with  two  molecules  of  sodium  bisulphite 
instead  of  with  but  one. 

Crotonic  aldehyde,  CH3.CH:  CH.CHO,  is  formed  by  heating 
aldol  (p.  82). 

Geranial  or  citral,  (CH3)2C:  CH.CH2.CH2.C(CH3):  CH.CHO, 
is  an  aldehyde  with  two  double  bonds,  which  is  found  in  various 
essential  oils,  such  as  those  of  orange  peel  and  citron.  It  is  a 
liquid  which  can  be  distilled  without  decomposition  only  under 
reduced  pressure.  It  is  used  in  the  manufacture  of  ionone,  a 
cyclic  compound,  which  is  the  artificial  oil  of  violets.  The  corres- 
ponding alcohol,  geraniol,  occurs  in  the  oils  of  geranium  (hence 
the  name)  and  of  roses. 

ALDEHYDES 

Boiling  Specific 

Point  Gravity 

Formaldehyde  HCHO  —21°  0.8153  (-20°) 

Acetaldehyde  CH3.CHO  20.8  0.780  (20°) 

Propionic  CH3.CH2.CHO  49  0.807  (20°) 

Butyric  CH3.CH2.CH2.CHO  74  0.817  (20°) 


3v 

Isobutyric  >  CH.CHO  63  0.794(20°) 

/ 


Valeric                   CH3.CH2.CH2.CH2.CHO  103  0.818(11.2°) 

CH3V 

Isovaleric                        >  CH.CH2.CHO  92  0.798(20°) 

CH37 

Caproic                 CH3(CH2)4.CHO  128  0.834  (20°) 

Acroleln                 CH2:CH.CHO  54.2  ........ 

Crotonic                CH3.CH:CH.CHO  103  0.856  (17°) 

Geranial  (citral)    C9Hi6.CHO  224-228  ........ 

Chloral                  CCl^.CHO  97  1.512(20°) 


INTRODUCTION    TO    ORGANIC    CHEMISTRY  §3 

KETONES 

Formula 

Acetone                                     CH3.CO.CH3  56.  0.812  (o°) 

Methyl-ethyl  Ketone               CH3.CO.C2H6  79.6  0.825(0°) 

Diethyl  Ketone                    C2H6.CO.C2H6  102.7  0.833(0°) 

Methyl-propyl  (n)  Ketone  CH3.CO.C3H7  102  0.808(20°) 

Methyl-isopropyl  Ketone    CH3.CO.CH(CH3)2  94-96  0.815(15°) 

Methyl-butyl  (n)  Ketone    CH3.CO.C4H9  127-128  0.830(0°) 

Methyl-butyl  (iso)  Ketone  CH3.CO.CH2.CH(CH3)2  116  0.819  (o°) 

Methyl-butyl(ter.)  Ketone  CH3.CO.C(CH3)3  106  0.826(0°) 

Ethyl-propyl  (n)  Ketone    C2H5.CO.C3H7  122-124  0.833(0°) 

Ethyl-propyl  (iso)  Ketone  C2H6.CO.CH(CH3)2  117-119  0.830(0°) 

Dipropyl  (n)  Ketone               C3H7.CO.C3H7  144  0.820(20°) 

Methyl-amyl  (n)  Ketone         CH3.CO.C6Hu  155-156  0.813  (o°) 

Ethyl-butyl  (iso)  Ketone        C2H5.CO.C4H9  135  0.829(0°) 

Ketones 

Ketones  are  the  first  oxidation  products  of  secondary  alcohols. 
The  simplest  ketone  possible,  therefore,  is  that  derived  from 
isopropyl  alcohol,  CHs.CH.OH.CHa  and  has  the  molecular  for- 
m.ula,  CsHeO.  From  our  knowledge  of  the  structure  of  secondary 
alcohols  and  the  discussion  of  the  structural  formula  of  aldehyde, 
we  should  naturally  give  this  ketone  the  formula,  CH3.CO.CH3. 
This  is  determined  to  be  the  correct  formula  by  its  reactions, 
especially  that  with  phosphorus  pentachloride  which  substitutes 
two  atoms  of  chlorine  for  one  of  oxygen.  Other  ketones  give 
similar  reactions;  hence  the  characteristic  group  of  a  ketone 
is  the  divalent  group  =  C  =  O  uniting  two  alkyls,  and  the  general 
formula  for  simple  ketones  of  this  series  is  CnH2n+2CO,  in 
which  n  is  not  less  than  two.  The  group  =  CO  is  called 
carbonyl. 

It  should  be  noticed  that  the  carbonyl  group  is  common  to  both 
ketones  and  aldehydes,  the  only  difference  in  their  formulas  being 
that  in  the  ketones  carbonyl  unites  two  alkyls,  and  in  the  alde- 
hydes, an  alkyl  and  a  hydrogen  atom. 


89  ALDEHYDES   AND   KETONES 

Acetone,  CH3.CO.CH3,  is  the  first  member  of  the  series  of 
saturated  ketones  and  is  typical  of  all  the  others.  It  is  ob- 
tained commercially  from  the  products  resulting  from  the  dis- 
tillation of  wood  (p.  59),  and  also  from  calcium  or  barium  acetate. 
Pure  acetone  is  made  by  distilling  the  crystalline  addition 
product  it  forms  with  sodium  sulphite  with  a  solution  of 
sodium  carbonate.  It  is  a  colorless  liquid  of  a  characteristic 
and  not  unpleasant  odor.  It  mixes  in  every  proportion  with 
water  and  can  be  separated  from  water  by  fractional  distillation. 
It  boils  at  56.5°.  Acetone  is  a  good  solvent  for  many  organic 
compounds,  and  for  gums,  resins,  etc.  It  is  used  as  a  solvent, 
and  also  in  the  preparation  of  chloroform,  iodoform,  sulphonal 
(p.  240),  and  other  compounds  used  in  medicine.  Acetone 
occurs  in  normal  urine  in  small  amounts,  and  is  present  in 
larger  quantities  in  certain  diseases,  especially  in  diabetes. 

Acetone  and  other  ketones  can  be  formed:  i.  From  the 
corresponding  alkyl  dihalides,  as  the  aldehydes  are: 

CH3.CC12.CH3  +  H2O  =  CH3.CO.CH3  +'2HC1 

2.  From  acid  chlorides  (p.  114)  by  zinc  alky  Is  or  magnesium 
alkyl  halides: 

2CH3.CO.C1  +  2C2H5MgI  =  2CH3.CO.C2H5  +  MgCl2  -f  MgI2 

Acetyl  chloride  Methyl-ethyl  ketone 

This  reaction  gives  a  method  by  which  mixed  ketones,  contain- 
ing two  different  alkyl  groups  can  be  made. 

3.  By  oxidation  of  secondary  alcohols  (p.  66): 

CH3.CHOH.CH3  +  O  ->  CH3.CO.CH3  +  H2O 

4.  From  calcium  salts  of  organic  acids  by  distillation: 

CH*COxS  "  CHa.CO.CH,  +  CaCO, 
"  CH,CO.C2H6  +  CaCO, 

But  in  the  second  reaction  the  two  simple   ketones,  acetone 

CH3.CO.CH3,  and  diethylketone  C2H5.CO.C2H5,  are  also  formed. 

We  have  seen  that  when  calcium  formate  is  heated  with  the 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  90 

salt  of  a  higher  acid,  the  chief  product  is  an  aldehyde  (p.  77). 
Aldehydes  may,  indeed,  be  viewed  as  mixed  ketones  in  which 
hydrogen  replaces  one  of  the  alkyl  groups.  In  fact,  the  first 
substance  corresponding  to  the  general  formula  CnH2n+2CO  is 
CH4CO  =  CH3.CHO  or  acetaldehyde.  The  general  formulas 
for  ketones  and  for  aldehydes  show  that  these  compounds,  when 
the  number  of  carbon  atoms  is  the  same,  are  isomeric,  both 
being  CnH2n+2CO,  and  are  only  distinguished  by  formulas 
containing  the  groups  characteristic  of  each. 

Nomenclature. — Acetone  was  the  first  ketone  known  and  its 
name  indicated  its  relation  to  the  acetates.  The  individual 
ketones  are  named  descriptively  from  the  alkyl  groups  they  con- 
tain— thus  acetone  is  dimethyl  ketone;  CH3.CO.C2H5,  methyl- 
ethyl  ketone,  etc.  Ketones  are  also  systematically  named  by 
adding  on  to  the  name  of  the  hydrocarbons  from  which  they 
are  theoretically  derived:  thus  CH3.CO.CH3  is  propanon, 
CH3CO.C2H5,  butanon,  etc. 

The  reactions  of  acetone  and  the  other  ketones  are  not  as  varied 
as  those  of  the  aldehydes.  Like  the  aldehydes,  their  oxygen  atom 
is  replaced  by  two  atoms  of  chlorine  or  bromine  through  the 
action  of  phosphorus  pentahalides;  they  form  addition  products 
with  hydrocyanic  acid  and  acid  sodium  sulphite  (but  only  when 
they  contain  the  group  CH3.CO),  and  with  nascent  hydrogen  (giv- 
ing secondary  alcohols);  with  Grignard's  reagent  they  yield 
tertiary  alcohols  (p.  37);  and  they  react  with  hydroxyiamine  and 
hydrazines,  forming  ketoximes  and  hydrazones.  But  unlike  the 
aldehydes,  the  ketones  are  not  easily  oxidized,  and  hence  are  not 
reducing  agents.  When  oxidation  occurs,  acids  of  a  less  number 
of  carbon  atoms  are  formed,  the  chain  of  carbon  atoms  breaking 
at  the  carbonyl  group.  When  reduced  by  sodium  amalgam, 
together  with  the  secondary  alcohol  appreciable  amounts  of 
dihydroxyl  tertiary  alcohols  are  formed,  called  pinacones: 

2CH3.CO.CH3  +  HH  =  (CH3)2C.C(CH3)2 

I    I 
HO  OH 


91  ALDEHYDES   AND   KETONES 

Ketones  give  no  addition  product  with  ammonia,  but  form  a 
number  of  complex  condensation  products  from  reaction  between 
two  or  more  molecules  and  ammonia,  e.g. : 

/CH3 

2CH3.CO.CH3  +  NH3  =  CH3.CO.CH2.C(-CH3  -f  H2O 

\NH2 

Diacetonamine 

Ketones  do  not  react  with  alcohols  and  acid  anhydrides  as 
aldehydes  do,  they  do  not  polymerize,  nor  do  they  give  resins  with 
alkalies. 

The  agreements  in  the  reactions  of  ketones  and  aldehydes  are 
conditioned  by  the  presence  of  the  carbonyl  group,  =C  =  O, 
which  is  common  to  both  classes  of  compounds;  the  differences 
are  due  to  the  fact  that  in  ketones  both  valencies  of  this  group  are 
united  to  alkyl  groups,  while  in  aldehydes  (except  formaldehyde 
which  shows  individual  peculiarities),  one  valence  is  satisfied  with 
hydrogen  and  the  other  with  an  alkyl  group. 

Identification. — Ketones  are  identified  by  the  formation  of  an 
oxime  (ketoxime)  or  phenylhydrazone,  or  a  crystalline  additive 
product  with  acid  sodium  sulphite  (if  they  contain  the  CH3.CO 
group),  while  they  do  not  reduce  Fehling's  solution,  or  silver  nitrate, 
or  produce  an  immediate  color  with  S drift's  reagent. 

Halogen  Derivatives  of  Aldehydes  and  Ketones 

Chloral,  CC13.CHO  (trichloraldehyde),  and  chloral  hydrate, 
CC13.CHO.H2O,  are  the  most  important  of  the  halogen  deriva- 
tives of  the  aldehydes.  Chloral  can  be  made  by  the  direct  action 
of  chlorine  on  aldehyde  in  dilute  solution;  but  the  best  method  for 
its  preparation  is  by  leading  chlorine  into  alcohol.  The  alcohol 
is  at  first  kept  cool  and  afterward  warmed  to  about  60°,  and  the 
current  of  chlorine  is  continued  until  it  is  no  longer  absorbed,  the 
operation  lasting  several  days.  The  product,  when  cool,  forms  a 
crystalline  mass  from  which,  on  treatment  with  concentrated 


INTRODUCTION    TO    ORGANIC    CHEMISTRY  9  2 

sulphuric  acid,  the  chloral  separates  as  an  oil,  and  is  purified  by 
distillation  from  calcium  carbonate. 

The  action  of  the  chlorine  on  alcohol  is  first  that  of  an  oxidizing 
agent,  producing  aldehyde: 

CH3.CH2OH  +  C12  =  CH3.CHO  +  2HC1 
Then  the  chlorine  replaces  hydrogen  in  the  methyl  group: 
CH3.CHO  +  3C12  =  CCla.CHO  +  3HC1 

Secondary  reactions,  however,  occur,  so  that  the  product  contains 
trichloracetalj  CCl3.CH(OC2H5)2,  from  reactions  of  aldehyde  and 
chlorine  with  unchanged  alcohol;  ethyl  chloride,  C2H5C1,  and 

/OH 
chloral  alcoholate,  CC13.CH  ,  from  decomposition  of  tri- 

\OC2H5 

chloracetal  by  the  hydrochloric  acid  which  is  formed;  and  chloral 
hydrate  by  union  of  chloral  with  the  water  present.  The  sul- 
phuric acid  which  is  added  sets  chloral  free  from  its  compounds. 

Properties  and  Reactions. — Chloral  is  an  oily  liquid  of  penetrat- 
ing odor;  it  boils  at  97.7°  and  its  specific  gravity  is  1.513  (20°). 
It  does  not  dissolve  in  water,  but  reacts  with  it  with  the  develop- 
ment of  much  heat  and  the  formation  of  the  hydrate.  Chloral 
hydrate,  which  is  the  form  in  which  chloral  is  usually  employed, 
is  given  the  formula,  CC13.CH(OH)2,  indicating  that  it  is  not  prop- 
erly a  hydrate,  or  compound  with  water  of  crystallization,  but  a 
definite  compound  with  two  hydroxyl  groups.  In  support  of  this 
view  are  the  facts  of  the  heat  produced  in  its  formation,  and  that 
it  does  not  give  the  aldehyde  reaction  with  Scruff's  reagent  (p.  86). 

Chloral  hydrate  forms  large  crystals,  which  melt  at  57°.  At 
96-98°  it  boils  with  decomposition  into  chloral  and  water.  It 
is  well  known  as  a  soporific. 

Chloral  and  chloral  hydrate  are  oxidized  by  nitric  acid  to  tri- 
chloracetic  acid,  CC13.CO.OH;  and  when  treated  with  alkalies 
give  chloroform  and  a  formate: 

CC13.CHO  +  KOH  =  CHC13  +  HCO.OK 


93  ALDEHYDES   AND   KETONES 

Chloral  is  probably  formed  as  an  intermediate  step  in  the  manu- 
facture of  chloroform  from  alcohol  by  means  of  bleaching  powder. 
The  course  of  this  reaction  is  commonly  represented  as  follows:  (i) 
Oxidation  of  alcohol  to  aldehyde,  (2)  chlorination  of  aldehyde 
to  chloral,  and  (3)  reaction  of  the  chloral  with  the  calcium  hydrox- 
ide present  in  bleaching  powder  with  the  formation  of  chloroform 
and  calcium  formate: 

1.  2CH3.CH2OH  +  Ca(OCl)2  =2CH3.CHO  +CaCl2  +  2H2O 

2.  2CH3.CHO      +  3Ca(OCl)2=2CCl3.CHO+3Ca(OH)2 

3.  2CC13.CHO     +Ca(OH)2    =2CHC13       +(HCO.O)2Ca 

Halogen  derivatives  of  ketones  are  readily  made  by  direct  sub- 
stitution; but  here,  as  generally  in  direct  replacements  of  hydrogen 
in  compounds  containing  two  or  more  carbon-hydrogen  groups,  it 
is  impossible  to  obtain  all  of  the  possible  chlorine  or  bromine  deriva- 
tives by  the  action  of  these  elements  on  the  ketone.  Sym- 
metrical dichloracetone,  CH2C1.CO.CH2C1,  is  not  formed  in  this 
way,  though  the  isomeric  compound,  CH3.CO.CHC12,  is  readily 
made. 

Trichloracetone  is  decomposed  by  alkalies  into  chloroform  and 
an  acetate,  and  this  reaction  is  probably  the  last  step  in  the 
preparation  of  chloroform  from  acetone  by  the  action  of 
bleaching  powder: 

2CH3.CO.CH3  +  3Ca(OCl)2  =  2CC13.CO.CH3  +  3Ca(OH)2 
2CC13.CO.CH3  +  Ca(OH)2    =  2CHC13  +  (CH3.CO.O)2Ca 


CHAPTER  VIII 
SIMPLE  MONOBASIC  ACIDS 

Acetic  acid  is  one  of  the  best-known  organic  acids,  and  since 
it  is  one  of  the  simplest  in  composition  and  structure  we  will 
begin  our  discussion  of  the  organic  acids  by  considering  its  prop- 
erties and  reactions.  Both  the  acid  and  its  salts  occur  in  small 
amounts  in  certain  plants.  Vinegar,  of  which  acetic  acid  is 
the  chief  acid  constituent,  has  been  known  from  the  earliest  times. 
The  two  chief  sources  of  acetic  acid  are  alcohol  and  wood.  The 
acid  is  obtained  in  many  instances  from  ethyl  alcohol  as  the 
result  of  an  oxidation  effected  by  means  of  a  bacterial  ferment 
(Bacterium  aceti).  These  bacteria  are  usually  present  in  the  air, 
and,  consequently,  dilute  solutions  of  alcohol  such  as  cider,  wines, 
etc.,  produced  by  the  alcoholic  fermentation  of  fruit  juices,  usu- 
ally become  sour  after  a  time  from  the  conversion  of  their 
alcohol  into  acetic  acid,  and  are  thus  changed  into  vinegar. 
The  slimy  substance  which  is  found  in  vinegar  barrels  contains 
the  bacteria  and  is  called  "  mo ther-of- vinegar."  The  oxygen  neces- 
sary for  the  change  is  supplied  by  the  air.  Solutions  containing 
more  than  about  10  per  cent,  of  alcohol  do  not  ferment,  nor  does 
fermentation  occur  in  dilute  solutions  unless  they  contain  small 
amounts  of  certain  substances — phosphates  and  nitrogen  com- 
pounds— which  are  essential  for  the  growth  of  the  organisms. 
This  method  of  making  acetic  acid  is  carried  on  commercially  by 
the  so-called  "quick  vinegar  process."  In  this,  dilute  alcohol, 
mixed  with  vinegar,  and  to  which  malt  or  beer  is  often  added,  is 
allowed  to  trickle  slowly  through  tall  vats  nearly  rilled  with  beech- 

94 


95  SIMPLE   MONOBASIC  ACIDS 

wood  shavings  which  have  been  covered  with  the  necessary  bac- 
teria by  previous  soaking  in  vinegar.  The  heat  produced  by  the 
oxidation  of  the  alcohol  causes  a  current  of  air  to  enter  by  perfora- 
tions in  the  bottom,  and  draw  up  through  the  vats;  and  the  tem- 
perature, which  should  be  about  30°,  is  regulated  by  controlling 
the  temperature  of  this  entering  air.  The  solutions  are  usually 
passed  through  several  vats  in  succession,  the  operation  taking 
eight  to  twelve  days,  until  most  of  the  alcohol  is  changed  into 
acid.  A  little  alcohol  is,  however,  always  left  unchanged,  be- 
cause with  its  total  disappearance  the  acetic  acid  would  begin  to 
be  itself  oxidized  into  carbon  dioxide  and  water. 

The  vinegar  thus  obtained  usually  contains  from  4  to  6  per 
cent,  of  acid,  though  it  is  sometimes  a  little  stronger.  It  is 
used  as  table  vinegar,  and  to  some  extent  in  making  white 
lead  by  the  Dutch  process.  Table  vinegar  contains  vari- 
ous substances  besides  acetic  acid,  which  give  it  its  aroma 
and  flavor  and  which  vary  with  the  source.  Thus  cider 
vinegar,  wine  vinegar,  and  malt  vinegar,  each  have  distinctive 
qualities.  Spirit  vinegar,  made  from  dilute  alcohol,  is  often 
colored  with  caramel  and  given  its  odor  and  flavor  by  adding  cer- 
tain esters. 

Acetic  acid  for  other  uses  than  the  above  is  mostly  obtained 
from  the  "pyroligneous  acid"  produced  in  the  dry  distillation 
of  wood.  The  acid  in  the  distillate  is  first  converted  into  calcium 
acetate,  and  from  this  the  commercial  acid  is  obtained  by  distil- 
lation with  sulphuric  acid  from  cast  iron  retorts,  or  with  concen- 
trated hydrochloric  acid  from  copper  retorts.  An  excess  of  hydro- 
chloric acid  must  be  avoided  so  that  none  of  it  shall  distil  with 
the  acetic  acid.  The  acid  thus  obtained  is  purified  by  redistilla- 
tion from  a  little  potassium  dichromate  (to  oxidize  impurities) 
and  by  filtering  through  charcoal.  The  ordinary  commercial  acid 
contains  about  30  per  cent,  of  the  pure  acid. 

For  the  purpose  of  preparing  the  pure  anhydrous  acid,  sodium 


INTRODUCTION  TO   ORGANIC   CHEMISTRY  96 

acetate  is  made,  purified  by  recrystallization,  heated  to  drive  off 
its  water  of  crystallization,  and  then  mixed  with  concentrated 
sulphuric  acid  and  distilled.  A  nearly  anhydrous  acid  is  thus 
obtained,  and  from  it  an  acid  entirely  free  from  water  is  prepared 
by  crystallization.  Its  molecular  formula  is  found  to  be  C2H4O2. 

Uses. — Acetic  acid  is  used  in  making  white  lead,  as  stated  above, 
in  the  dye-stuff  industry,  and  for  making  a  number  of  salts  of 
practical  value:  lead  acetate  or  "sugar  of  lead,"  "verdigris,"  a 
basic  acetate  of  copper,  "Paris  green,"  a  double  salt  of  copper 
acetate  and  arsenite,  and  the  acetates  of  iron,  chromium,  and 
aluminium,  which  are  extensively  used  as  mordants  in  dyeing  and 
calico  printing. 

In  the  laboratory  the  pure  acid  is  used  as  an  excellent  solvent 
for  many  carbon  compounds. 

Properties  of  Acetic  Acid. — Pure  anhydrous  acetic  acid  is  a  color- 
less liquid  at  temperatures  above  16.675°,  which  is  the  melting 
point  of  the  crystalline  solid  formed  at  lower  temperatures.  From 
the  resemblance  of  the  solid  acid  to  ice  the  anhydrous  acid  is 
often  called  "glacial"  acetic  acid.  The  boiling  point  is  118°. 
The  anhydrous  acid  and  mixtures  with  small  amounts  of  water 
show  in  a  pronounced  degree,  the  phenomenon  of  supercooling, 
which  is  common  to  many  liquids  and  solutions.  The  addition 
of  a  crystal  of  the  acid  is  usually  necessary  to  cause  the  crystalli- 
zation to  take  place,  and  when  it  occurs  the  temperature  rises  to 
the  "freezing  point."  The  freezing  point  of  mixtures  of  acid  and 
water  (the  temperature  at  which  some  separation  of  solid  occurs) 
is  lower  as  the  proportion  of  water  increases,  until  with  40  per 
cent,  of  water  a  minimum  is  reached  at  —  26.75°.  From  solu- 
tions less  dilute  than  this,  the  anhydrous  acid  separates  at  the 
freezing  point,  while  from  more  dilute  solutions  ice  is  formed. 
From  the  mixture  containing  40  per  cent,  of  water,  acid  and  water 
crystallize  together  and  the  temperature  remains  unchanged 
till  the  whole  is  solid.1  When  the  anhydrous  acid  is  mixed  with 

1  See  a  Physical  Chemistry  for  discussion  of  cryohydrates. 


97  SIMPLE   MONOBASIC   ACIDS 

water  there  is  contraction  of  volume  and  tjie  temperature  rises. 
The  specific  gravity  increases  as  the  acid  is  diluted,  until  (at  15°) 
with  77-80  per  cent,  of  acid  a  maximum  is  reached.  A  solution 
containing  43  per  cent,  has  the  same  specific  gravity  at  15°  as  the 
anhydrous  acid;  and  there  are  two  solutions  of  different  strengths 
for  all  specific  gravities  between  this  (1.055)  and  the  maximum 
(1-075). 

Acetic  acid  does  not  form  a  constant  boiling-point  mixture  with 
water  as  the  halogen  acids  (and  formic  acid)  do,  but  the  distillate 
becomes  more  and  more  dilute,  while  a  stronger  and  stronger  acid 
remains  in  the  flask. 

Glacial  acetic  acid  blisters  the  skin,  and  has  a  penetrating  and 
characteristic  odor.  It  is  not  inflammable  until  heated  nearly  to 
the  boiling  point,  when  the  vapor  burns  wjth  a  pale  blue  flame. 
The  acid  mixes  with  water,  alcohol  and  ether  in  all  proportions, 
and  its  aqueous  solutions  are  sharply  acid.  Acetic  acid  dissolves 
very  many  organic  compounds  (without  acting  on  them  chem- 
ically) and  some  inorganic  substances  which  are  insoluble  in  water, 
as,  for  instance  iodine  and  sulphur. 

It  acts  on  certain  metals  and  dissolves  the  hydroxides  of  metals, 
readily  forming  acetates.  Acetic  acid  is  an  unusually  stable 
organic  compound.  Its  vapor  is  hardly  decomposed  when  led 
through  a  red-hot  tube;  it  withstands  oxidizing  agents  to  a  re- 
markable degree,  and  is  hence  a  frequent  product  of  the  oxidation 
of  more  complicated  compounds.  On  this  account  it  may  be 
employed  as  a  solvent  for  chromic  acid  when  this  is  to  be  used  to 
oxidize  a  substance  insoluble  in  water. 

Structure  of  Acetic  Acid. — From  the  molecular  formula  of 
acetic  acid,  C2H4O2,  we  can  make  three  simple  structural  formulas: 

CH3                    CH3                 CH2OH  CH.OH 

I  or       |                  ,|  ,     and        || 

C=O              C=O.OH        C=O  CH.OH 
\OH                                        \H 


INTRODUCTION  TO   ORGANIC  CHEMISTRY  98 

The  third  formula  is  that  of  an  unsaturated  dihydroxyl  alcohol, 
and  the  second  is  a  mixed  alcohol  and  aldehyde.  Acetic  acid 
shows  none  of  the  properties  of  such  compounds:  it  does  not  give 
the  reactions  peculiar  to  unsaturated  compounds,  it  has  no 
alcohol  characteristics,  and  it  is  not  a  reducing  agent  as  it  should 
be  if  it  contained  an  aldehyde  group.  As  it  is  formed  by  the 
oxidation  of  ethyl  alcohol,  CH3.CH2OH,  or  of  its  first  oxidation 
product  aldehyde,  CH3.CHO,  the  first  formula  is  the  one  naturally 
suggested,  i.  Analysis  of  its  salts  show  that  it  is  a  monobasic 
acid,  which  means  that  one  hydrogen  atom  is  differently  combined 
from  the  other  three.  2.  Chlorine  replaces,  one  after  the  other, 
three  and  only  three  of  the  hydrogen  atoms.  This  indicates  the 
methyl  group,  CH3.  3.  Phosphorus  chlorides  substitute  one 
chlorine  atom  for  one  atom  each  of  hydrogen  and  oxygen;  hence 
an  hydroxyl  group  is  present.  The  only  possible  structure  with 
a  methyl  and  a  hydroxyl  group  is  CH3.C  =  O.OH.  Further,  acetic 
acid  may  be  made  by  the  action  of  potassium  hydroxide  in 
alcoholic  solution  on  trichlor-ethane,  CH3.CC13.  We  may 
picture  this  reaction  as  first  giving  CH3.C(OH)3  followed  by 
the  breaking  down  of  this  unstable  compound  into  acetic  acid  and 
water: 

/OH 
- 


=  CH3.CO.OH  +  H2O. 
\OH 

This  structure  accords  with  all  the  reactions  of  acetic  acid  and 
all  the  methods  of  its  formation.  The  monad  group  —  C  =  O.OH 
which  contains  the  acid  hydrogen  atom  of  acetic  acid  is  called 
the  carboxyl  group  (carbonyl  and  hydxoxyl)  and  is  the  charac- 
teristic group  of  all  organic  acids. 

Laboratory  Methods  for  the  Formation  of  Acetic  Acid  and  its 
Homologues.  —  The  most  important  reactions  which  result  in  the 
formation  of  acetic  acid  and  which  are  also  general  reactions  for 
the  formation  of  its  homologues,  are: 


Q9  SIMPLE   MONOBASIC   ACIDS 

1.  Oxidation  of  the  primary  alcohols  or  aldehydes  (already 
described). 

2.  Hydrolysis  of  an  alkyl  cyanide  (acid  nitrile)  (p.  153) : 

CH3.CN  +  2H20  =  CH3.CO.OH  +  NH3 

Methyl  cyanide  Acetic  acid 

The  alkyl  cyanides  are  produced  by  the  action  of  potassium  cyan- 
ide and  alkyl  iodides: 

CH3I  +  KCN  =  CH3.CN  +  KI 

The  hydrolysis  of  the  alkyl  cyanide  is  effected  most  rapidly  by 
boiling  the  cyanide  with  dilute  sulphuric  or  hydrochloric  acid,  or 
a  dilute  alkali  (cf.  the  formation  of  formic  acid  p.  102). 

3.  From  esters  by  hydrolysis  with  water  or  caustic  alkalies: 

CH3.CO.OC2H5  +  H2O   <r±CH3.CO.OH  +  C2H5OH 

Ethyl  acetate 

CH3.CO.OC2H5  +  KOH  =  CH3.CO.OK  +  C2H6OH 

In  the  second  reaction  the  acetate  is  of  course  obtained,  from 
which  the  acid  is  readily  set  free  by  hydrochloric  or  sulphuric 
acid. 

4.  From  trihalides  by  hydrolysis  (p.  4ia): 
CH3.CC13  +  4KOH  ->  CH3.CO.OK  +  3KC1  +  2H2O 

5.  By  heating  dibasic  acids  which  contain  two  carboxyl  groups 
united  to  the  same  carbon  atom: 

CH2:(CO.OH)2  =  CH3.CO.OH  +  CO2 

Malonic  acid 

6.  From  alkyl  halides  by  the  Grignard  reaction  (p.  37). 
Reactions   of  Acetic  Acid. — The   hydrogen   of   the  hydroxyl 

group  can  be  replaced: 

1.  By  metals  with  the  formation  of  salts. 

2.  By  alkyl  groups,  giving  esters, 

CH3.CO.OH+  C2H6OH  <=±  CH3.CO.OC2H6-fH2O 

Ethyl  acetate 

3.  The  hydroxyl  group  may  be  replaced  by  chlorine  or  bromine 
(by  phosphorus  halides)  giving  the  acid  halides: 

3CH3.CO.OH  +  2PC13  =  3CH3.CO.C1  +  3HC1  +  PiO« 
CH3.CO.OH+    PC16=    CHa.CO.Cl  +  POClj  +  HC1 

Acetyl  chloride 


INTRODUCTION  TO   ORGANIC   C 


4.  The  hydrogen  of  the  methyl  group  can  be  directly  replaced 
by  chlorine  or  bromine,  yielding  mono-,  di-,  and  tri-halogen 
acetic  acids: 

CH2C1.CO.OH,  CHC12.CO.OH,  CC13.CO.OH 

Reactions  of  Acetates.  —  Among  the  important  reactions  into 
which  acetates  enter  are: 

1.  The  formation  of  the  acid  amide  (p.  137)  by  heating  ammo- 
nium acetate: 

CH3.CO.ONH4  =  CH3.CO.NH2  +  H2O 

Acetamide 

By  distillation  of  the  acid  amide  with  phosphorus  pentoxide 
the  nitrile  of  the  acid  (an  alkyl  cyanide)  is  formed: 

P205 

CH3.CO.NH2  ->  CH3.CN  +  H2O 

2.  The  formation  of  aldehyde  by  heating  a  mixture  of  calcium 
acetate  and  formate  ;  or  of  a  ketone  when  calcium  acetate  is  heated 
alone  or  with  homologous  calcium  salts  of  higher  atomic  weights 
(pp.  77,  89). 

3.  The  formation  of  methane  by  replacement  of  the  carboxyl 
group  with  hydrogen,  when  sodium  acetate  is  heated  with  sodium 
hydroxide  or  soda-lime  (p.  26): 

CHs.CO.ONa  +  NaOH  =  CH4  +  Na2CO3 

4.  The  formation  of  ethane  by  electrolysis  (p.  29). 

Other  Acids  of  the  Type  of  .Acetic  Acid.  —  A  large  number  of 
organic  acids  are  known,  in  each  of  which  one  carboxyl  group  is 
united  to  an  alkyl  group  (or  hydrogen).  They  form  an  homologous 
series,  whose  general  formula  is  CnH2n+ICO.OH. 

General  Properties  of  the  Acids.  —  The  acids  of  this  series,  which 
contain  less  than  ten  atoms  of  carbon,  are  liquids  at  ordinary 
temperatures,  and  those  of  greater  molecular  weight  solids.  As 
the  molecular  weight  increases,  the  liquid  acids  become  oily  and 
less  soluble  in  water,  and  the  specific  gravity  decreases.  All 
except  the  first  three  are  lighter  than  water.  The  solid  acids 


IO1 


'SIMPLE   MONOBASIC   ACIDS 


have  a  waxy  or  fatty  consistency  and  are  insoluble  in  water  but 
are  all  soluble  in  alcohol  and  in  ether.  All  except  the  highest  boil 
without  decomposition,  and  the  boiling  points  are  higher  with 
greater  molecular  weights.  The  melting  points  of  the  acids 
exhibit  an  interesting  periodicity,  alternately  rising  and  sinking  as 
the  molecular  weights  become  larger;  the  acids  with  an  even  num- 
ber of  carbon  atoms  always  having  higher  melting  points  than  the 
acids  containing  an  odd  number  of  carbon  atoms  which  are  next 
above  them  in  the  series.  The  acids  containing  from  four  to  nine 
carbon  atoms  have  a  disagreeable  odor  like  that  of  rancid  butter. 
The  acid  character  becomes  less  and  less  pronounced  as  the  molec- 
ular weight  is  greater,  and  the  higher  members  of  the  series  show 
that  they  are  acids  only  by  the  formation  of  salts.  The  salts  of 
the  lower  members  are  all  soluble  in  water,  but  with  the  higher 
members  only  the  alkaline  salts  dissolve. 

Their  reactions  are  similar  to  those  of  acetic  acid  and  the  ace- 
tates. It  should  be  remarked,  however,  that  chlorine  and  bro- 
mine replace  the  hydrogen  nearest  the  carboxyl  group,  thus 
giving  a-substitution  products. 

NORMAL  MONOBASIC  ACIDS 


Name            Radical    with 
CO.  OH  group 

Melting 
Point 

Formic 

H 

8.6° 

Acetic 

CH3 

I6.7 

Propionic 

C2H6 

—  22 

Butyric 

C3H7 

-   7-9 

Valeric 

C4H9 

-58.5 

Caproic 

CsHn 

—  1.5 

Heptylic 

C6H13 

-10.5 

Caprylic 

C7H15 

16.5 

Pelargonic 

C8Hi7 

12.5 

Capric 

C9Hi9 

31.4 

Laurie 

CUH23 

48 

Palmitic 

Ci5H31 

62.6 

Margaric 

Ci6H33 

60 

Stearic 

CnH35 

69-3 

Cerotic 

C26H63 

78° 

Boiling 
Point 

Specific 
Gravity 

101° 

I 

•  231  ( 

10°) 

Il8.5                   I 

.0515 

dS°) 

141 

0 

.9985 

(14°) 

162 

O 

•9599 

(i9-i°) 

186 

0 

.9560 

(o°) 

205 

o 

•9450 

(o°) 

223 

o 

.9186 

(17.2°) 

237-5              o 

.9100 

(20°) 

254 

o 

.9110 

(m.p.) 

260 

«wy 

225 

«H 

268 

l°>    ° 

8527 

(m.p.) 

277 

3  3 

287    . 

o 

8454 

(m.p.) 

INTRODUCTION  TO   ORGANIC   CHEMISTRY  IO2 

All  the  normal  acids  up  to  Ci9H39.CO.OH  are  known.  The  acid 
of  largest  molecular  weight  which  is  known  is  C33H67.CO.OH. 
Isomeric  acids  corresponding  to  the  isomeric  primary  alcohols 
can  all  be  made. 

Nomenclature. — The  usual  names  of  the  acids  of  this  series  are 
the  original  names  which  are  often  suggested  by  the  sources  from 
which  the  acids  were  first  obtained.  Thus  formic  acid  from  ants 
(formica),  acetic  from  vinegar  (acetum),  butyric  from  butter, 
palmitic  from  palm  oil,  stearic  from  tallow  (ST«X,/O),  oleic  from  oils, 
etc.  A  systematic  method  of  naming  which  is  of  ten' employed, 
and  which  has  the  advantage  of  being  descriptive  of  the  structure, 
is  one  which  regards  them  (except  formic  acid)  as  derivatives  of 
acetic  acid:  thus  propionic  acid,  CH3.CH2.CO.OH,  is  methyl 
acetic  acid;  normal  butryic  acid,  CH3.CH2.CH2.CO.OH  is  ethyl 
acetic  acid;  and  iso-butyric  acid  (CH3)2CH.CO.OH,  is  dimethyl 
acetic  acid.  Another  systematic  nomenclature  changes  the  name 
of  the  hydrocarbon  of  the  same  number  of  carbon  atoms,  of  which 
the  acid  is  a  theoretical  derivative,  by  substituting  oic  for  the  final 
e;  thus  acetic  acid  is  ethanoic  acid,  etc.  The  name  of  fatty  acids  is 
often  given  to  the  series,  from  the  fact  that  esters  of  some  of  the 
higher  members  occur  in  the  fats,  and  many  of  the  acids  themselves 
resemble  fats. 

Formic  acid,  HCO.OH,  the  first  member  of  the  series,  is  found 
in  ants  (formica),  bees,  and  in  stinging  nettles.  The  irritation 
from  the  sting  of  these  is  probably  due  to  the  formic  acid  which 
they  deliver.  Formic  acid  occurs  also  in  many  insects  and  plants, 
and  is  frequently  one  of  the  products  formed  in  the  destructive 
distillation  and  oxidation  of  many  organic  substances.  Formic 
acid,  or  its  alkaline  salts  (from  which  the  acid  is  readily  set  free 
by  hydrochloric  acid)  can  be  made  in  the  laboratory  by  many 
reactions.  Some  of  them  are: 

1.  By  the  oxidation  of  a  solution  of  methyl  alcohol. 

2.  By  the  hydrolysis  of  hydrocyanic  acid  by  means  of  dilute 
alkalies  or  acids: 

HCN  +  2H2O  =  H.CO.OH  +  NH3 


103  SIMPLE    MONOBASIC    ACIDS 

If  an  acid  is  employed  the  products  are  formic  acid  and  the  am- 
monium salt  of  the  acid;  with  an  alkali,  the  alkaline  formate  and 
ammonia  are  produced. 

3.  By  warming  chloroform  with  an  alkali, 

CHC13  +  4KOH  =  H.CO.OK  +  3KC1  +  2H2O 
This  reaction  may  be  regarded  as  taking  place  in  three  steps: 

/OH 

CHC13  +  3KOH  =  3KC1  +  CH^OH; 

\OH 
/OH 
CH^-OH  =  HCO.OH  +  H2O; 

\OH 
HCO.OH  +  KOH  =  HCO.OK  +  H2O. 

Two  further  reactions  by  which  salts  of  formic  acid  can  be 
formed  from  the  elements  are  of  special  interest.  These  are: 

4.  By  the  action  of  moist  carbon  monoxide  on  solid  potassium 
or  sodium  hydroxide  at  a  temperature  of  about  200°: 

CO  +  NaOH  =  HCO.ONa 

This  reaction  is  employed  in  the  commercial  preparation  of  sodium 
formate,  the  carbon  monoxide  from  generator  gases  being  used 
under  pressure. 

5.  Moist  carbon  dioxide  acts  slowly  on  potassium,  forming  a 
mixture  of  the  acid  carbonate  and  the  formate: 

2CO2  +  2K  +  H2O  =  HCO.OK  +  KHCO3 

6.  Formates  are  also  produced  by  the  reduction  of  solutions  of 
ammonium  carbonate  or  of  acid  carbonates  by  means  of  sodium 
amalgam. 

Preparation. — None  of  the  above  -reactions  are,  however, 
usually  employed  for  laboratory  preparation  of  formic  acid;  but 
the  acid  is  made  by  distilling  a  mixture  of  glycerol  (glycerine)  and 


INTRODUCTION  TO   ORGANIC   CHEMISTRY  104 

oxalic  acid.  Oxalic  acid  when  heated  alone  gives  a  small  amount 
of  formic  acid  together  with  carbon  dioxide: 

C2H2O4  =  HCO.OIJ  +  CO2 

but  most  of  the  oxalic  acid  sublimes  unchanged.  When  mixed 
with  glycerol,  however,  the  reaction  goes  on  quite  readily  and 
completely.  The  glycerol  prevents  the  sublimation  of  the  oxalic 
acid  through  the  formation  of  a  formic  acid  ester  of  glycerol, 
which  then  breaks  down  through  hydrolysis  with  the  water 
present  into  formic  acid  and  glycerol. 

The  reactions  which  occur  at  about  120°  with  a  mixture  of 
equal  parts  of  glycerol  and  crystallized  oxalic  acid  are: 

CH2OH  CH2O.OCH 

CHOH    +     CO.OH  =    CHOH  +  CO2  +  H2O 

I  I  I 

CH2OH  CO.OH        CH2OH 

Glycerol  Oxalic  acid  Glyceryl  monoformate 

Very  little  formic  acid  distils  until  another  portion  of  oxalic 
acid  is  added,  when  by  the  reaction  between  the  monoformate 
and  the  crystallization  water  of  the  oxalic  acid  formic  acid  is  set 
free  and  at  the  same  time  the  monoformate  is  reproduced: 

CH2O.OCH  CH2OH 

CHOH          +  H2O  =  CHOH  +  HCO.OH 

I  I 

CH2OH  CH2OH 

By  adding  fresh  portions  of  oxalic  acid  from  time  to  time  the 
production  of  formic  acid  goes  on  indefinitely. 

When  oxalic  acid  and  four  times  its  weight  of  glycerol  are  heated 
and  the  temperatures  brought  up  to  22o°-26o°,  a  deeper-seated 
decomposition  of  the  formic  acid  ester  occurs  with  the  formation 
and  distillation  of  ally!  alcohol  (p.  69): 


105  SIMPLE   MONOBASIC   ACIDS 

CH2O.OCH      CH2 

I  II 

CHOH          =   CH         -f  CO2  +  H2O 

I  I 

CH2OH  CH2OH 

Glycerol  monoformate         Allyl  alcohol 

Anhydrous  formic  acid  cannot  be  obtained  by  distillation.  It 
can  be  prepared  from  anhydrous  lead  formate  by  the  action  of 
hydrogen  sulphide;  but  more  conveniently  by  using  anhydrous 
oxalic  acid  as  a  dehydrating  agent. 

The  structure  shown  by  the  formula  which  has  been  used  in  the 
description  of  the  methods  for  making  formic  acid  is  directly 
indicated  by  some  of  these  reactions,  and  is  in  accord  with  all  the 
known  facts  about  the  acid.  The  characteristic  acid  group, 
—  CO.OH,  is  here  combined  with  hydrogen  instead  of  an  alkyl 
group  as  in  acetic  acid  and  the  other  acids  of  this  series,  and  in 
this  fact  we  have  an  explanation  of  some  methods  of  formation 
and  some  reactions  which  differ  from  those  of  the  other  acids  of 
this  series.  Attention  is  called  especially  to  the  presence  of  the 
aldehyde  group  shown  in  the  structural  formula, 

H 


=  o 

OH 

Formic  acid  is  thus  both  an  acid  and  an  aldehyde. 

Properties. — Formic  acid  is  a  colorless  liquid  which  fumes 
slightly  in  the  air  and  is  hygroscopic.  It  is  heavier  than  water, 
solid  below  8. 6°  and  boils  at  101°.  When  mixtures  of  the  acid  and 
water  are  distilled,  they  behave  like  solutions  of  hydrochloric  acid, 
— both  strong  and  weak  solutions  giving  finally  a  mixture  whose 
boiling  point  (about  107°)  and  composition  (about  77  per  cent, 
acid)  are  constant  while  the  pressure  remains  unchanged.  The 
acid  has  an  irritating  odor,  and  the  pure  acid  in  contact  with  the 


INTRODUCTION  TO   ORGANIC   CHEMISTRY  106 

skin  causes  blisters  and  painful  wounds.  It  mixes  with  water  and 
with  alcohol  in,  all  proportions,  and  its  solutions  show  a  strong 
acid  reaction  with  litmus.  Formic  acid  is,  in  fact,  the  strongest 
of  the  organic  acids.  The  liquid  acid  does  not  burn,  but  its  vapor 
burns  readily  with  a  blue  flame  into  water  and  carbon  dioxide; 
and  solutions  of  the  acid  are  easily  oxidized  by  various  agents  and 
yield  the  same  products.  Formic  acid  is,  therefore,  a  strong 
reducing  agent.  It  precipitates  silver  and  mercury  when  warmed 
with  neutral  solutions  of  their  salts.  This  reducing  power,  which 
is  not  shown  by  the  other  acids  of  this  series,  is  like  that  shown 
by  the  aldehydes  (p.  78);  and  as  has  been  pointed  out,  the  acid 
contains  an  aldehyde  group  united  with  hydroxyl.  Formic  acid, 
from  this  point  of  view,  may  be  regarded  as  an  aldehyde  deriva- 
tive of  carbonic  acid: 

OH  OH 


OH  H 

Carbonic  acid  Formic  acid 

The  production  of  formates  by  the  reduction  of  carbonates 
(p.  103)  agrees  with  this  view,  since  the  aldehydes  may  be  regarded 
as  derived  from  the  corresponding  acids  by  the  withdrawal  of  an 
atom  of  oxygen. 

Reactions.  —  Formic  acid  is  decomposed  into  carbon  dioxide 
and  hydrogen  when  heated  to  160°  in  a  closed  vessel;  and  with 
concentrated  sulphuric  acid  the  acid  (and  of  course,  its  salts) 
decompose  readily  into  carbon  monoxide  which  is  evolved,  and 
water  which  is  held  by  the  sulphuric  acid.  Some  contact  agents 
such  as  finely  divided  rhodium,  cause  a  spontaneous  decomposi- 
tion of  the  same  sort. 

The  salts  of  formic  acid  —  the  formates  —  are  all  soluble  in  water, 
though  some,  such  as  the  silver  and  lead  formates,  do  not  dissolve 
very  freely. 


107  SIMPLE   MONOBASIC  ACIDS 

Formates  are  decomposed  by  heating.  The  alkali  salts  when 
carefully  heated,  and  the  salts  of  the  alkaline  earths  under  all 
conditions,  give  carbonates: 

**«,,  +  H,  +  CO 


though  by  rapidly  raising  the  temperature  to  400°,  in  the  absence 
of  air,  the  alkali  formates  yield  oxalates  and  hydrogen  : 

HCO.ONa 
HCO.ONa  = 

Ammonium  formate  gives  neither  carbonate  nor  oxalate  when 
heated,  but  at  230°  loses  the  elements  of  water  with  the  pro- 
duction of  formamide  HCO.NH2. 

Formic  acid  and  formates  may  be  identified  by  the  reactions 
with  concentrated  sulphuric  acid,  and  with  an  ammoniacal 
solution  of  silver  nitrate.  Either  alone  is  inconclusive,  because 
given  by  other  substances,  but  if  in  the  first  the  substance  does 
not  blacken  and  a  gas  is  obtained  which  burns  with  a  blue  flame; 
and  silver  is  precipitated  in  the  second,  formic  acid  or  a  formate 
is  present. 

Higher  Fatty  Acids 

These  may  be  made  by  the  general  methods  which  have  been 
given.  The  three  normal  acids  which  follow  acetic  acid  in  the 
series  are  also  formed  by  processes  of  fermentation. 

Propionic  Acid,  CH3.CH2.CO.OH  (methyl  acetic  acid  or 
propanoic  acid).  —  The  original  name  of  this  acid  was  -given  it 
as  the  first  01  the  series  which  showed  fat-like  properties  (TTP&TOS 
and  iriov).  It  is  found  in  small  quantities  in  wood  vinegar,  and 
is  formed  in  a  fermentative  process  which  takes  place  in  solu- 
tions of  the  calcium  salts  of  malic  and  lactic  acids.  It  is  also  a 
reduction  product  of  lactic,  glyceric,  acrylic  and  propargylic 
acids. 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  108 

Butyric  Acids.— Normal  butyric  acid,  CH3.CH2.CH2.CO.OH, 
ethyl  acetic  acid,  is  found  in  rancid  butter.  Its  glyceryl  ester 
forms  about  5  per  cent,  of  butter  fat,  which  is  made  up  of  this  and 
of  esters  of  several  other  acids  of  this  series.  The  acids  may  be 
set  free  from  these  esters  by  hydrolysis;  but  on  account  of  the 
difficulty  of  separation  this  is  not  a  favorable  method  for  obtain- 
ing butyric  acid. 

It  is  produced  by  the  action  of  a  special  ferment  (butyric  fer- 
ment) contained  in  old  Limburger  cheese  (which  also  contains  the 
acid),  on  sugars,  lactic  acid,  and  other  substances.  This  fermenta- 
tive process  is  the  one  usually  employed  for  its  preparation. 

Isobutyric  acid  (CH3)2  :CH.CO.OH,  dimethyl  acetic  acid,  is 
apparently  not  formed  by  fermentation.  It  occurs  in  consider- 
able quantities  in  the  juices  of  "St.  John's  bread,"  the  fruit  of 
the  carob  tree,  and  can  be  obtained  from  this  source  by  distillation 
with  water. 

Both  the  acid  and  an  ester  occur  in  aconite  root,  and  in  some 
other  substances.  Isobutyric  acid  is  much  less  soluble  in  water 
than  the  normal  acid,  and,  as  is  the  rule  with  iso-compounds,  its 
boiling  point  is  lower. 

Valeric  Acid. — -There  are  four  valeric  acids,  C^g.CO.OH, 
known,  all  that  are  structurally  possible.  The  normal  acid  is  in 
wood  vinegar  in  small  amounts  and  is  formed  in  a  fermentation 
of  calcium  lactate  solution.  One  of  the  iso-acids  is  found  in  the 
roots  of  valerian  (hence  the  name),  and  angelica,  and  may  be 
obtained  from  these  by  distillation  with  water.  It  is  optically 
active. 

Palmitic  Acid,Ci5H3iCO.OH,  and  Stearic  Acid,Ci7H35CO.OH. 
— Glyceryl  esters  of  the  normal  acids,  together  with  that  of  oleic 
acid  (p.  no),  are  the  chief  constituents  of  animal  fats,  and  are 
contained  in  many  vegetable  fats  and  oils.  The  acids  are  ob- 
tained from  these  sources,  commercially,  by  hydrolysis  of  the 
esters  (p.  124).  After  the  crystallization  of  the  two  solid  acids, 
the  liquid  oleic  acid  is  removed  from  them  by  hydraulic  pres- 


SIMPLE   MONOBASIC   ACIDS 

sure.  The  mixture  of  palmitic  and  stearic  acids  thus  obtained 
is  known  by  the  trade  name  of  "stearin"  (not  to  be  confused 
with  stearin  as  used  in  chemistry,  which  is  the  name  given  to 
the  glyceryl  ester  of  stearic  acid).  This  "  stearin,"  mixed  with 
paraffin  to  prevent  crystallization  and  consequent  brittleness, 
is  largely  used  for  making  candles. 

Palmitic  and  stearic  acids  are  colorless,  waxy  solids  which  melt 
at  63°  and  69°  respectively,  and  can  be  distilled  without  decompo- 
sition only  in  a  partial  vaccuum. 

Soaps.  —  The  salts  of  the  three  acids  whose  esters  form  the  fats 
are  called  soaps,  though  in  the  common  use  of  the  word,  only  the 
alkali  salts  are  meant.  Soap  is  made  by  the  decomposition  of 
the  esters  (fats)  by  solutions  of  the  alkalies,  the  alkali  salts  and 
glycerol  being  produced  in  equivalent  amounts: 


Stearin  Potassium  stearate  Glycerol 

When  potassium  hydroxide  is  used,  the  salts  with  the  glycerol 
form  a  jelly-like  mass  which  is  known  as  soft-soap;  when  the  fats 
are  boiled  with  sodium  hydroxide,  a  hard  soap  is  formed,  which 
is  precipitated  from  the  solution  by  adding  common  salt  and  cool- 
ing, while  the  glycerol  is  left  in  solution.  Transparent  soaps  are 
made  by  dissolving  a  hard  soap  in  alcohol  and  evaporating  the 
clear  solution.  Common  soaps  are  made  from  many  different 
materials  and  often  contain  various  additions.  Pure  soaps  are 
soluble  in  alcohol,  and  dissolve  in  water  with  some  hydrolysis  or 
separation  into  alkali  and  insoluble  acid.  The  soaps  of  the  alka- 
line earths  and  of  other  metals  are  insoluble;  hence  a  precipitate 
of  calcium  and  magnesium  salts  is  produced  when  soap  is  used  with 
hard  water  and  the  formation  of  a  lather  is  prevented  until  the 
precipitation  is  complete.  The  method  for  determining  the 
hardness  of  a  water  is  based  on  this  reaction  —  a  soap  solution  of 
known  strength  being  added  to  a  measured  quantity  of  water, 
till  a  permanent  lather  is  produced  on  shaking.  The  cleansing 
action  of  soap  has  been  the  subject  of  such  dispute.  It  appears 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  IIO 

to  be  due  chiefly  to  the  power  which  soap  solutions  have  of  emulsi- 
fying oily  substances,  of  wetting  and  penetrating  into  oily  textures, 
and  of  lubricating  texture  and  impurity  so  that  the  impurity  is 
readily  removed.1 

Unsaturated  Acids 

Olei'c  acid,  whose  glyceryl  ester  occurs  in  fats  and  oil,  is  an 
unsaturated  acid  with  a  double  bond  between  two  of  its  carbon 
atoms: 

Ci7H33.CO.OH,  or   CH3(CH2)7CH  :CH(CH2)7CO.OH. 

The  position  of  the  double  bond  is  indicated  by  the  study  of 
the  compounds  (acids)  obtained  by  its  oxidation,  on  the  assump- 
tion that  the  break  caused  by  oxidation  occurs  at  this  place. 

Oleic  acid  is  an  oily,  odorless  liquid,  insoluble  in  water.  When 
cooled  it  crystallizes,  and  melts  at  14°.  It  readily  oxidizes  in 
contact  with  air,  becoming  brown  and  rancid. 

Both  ole'ic  acid  and  its  glyceryl  ester  are  changed  into  solids  by 
a  small  amount  of  nitrous  acid.  These  solids  have  the  same 
composition  as  the  original  substances,  and  are  called  ela'idic  acid 
and  ela'idin,  respectively.  The  reaction  is  used  in  the  examination 
of  oils  as  an  indication  of  the  amount  of  plein  they  contain. 

Acrylic  acid,  CH2  :  CH.CO.OH,  is  to  be  regarded  as  the  oxida- 
tion product  of  allyl  alcohol  (p. 69)  or  of  acrylic  aldehyde  (acrolein, 
p.  86).  It  is  the  first  acid  of  the  series  of  acids  with  a  double 
bond,  as  allyl  alcohol  is  the  first  alcohol.  It  can  be  formed  from 
the  corresponding  saturated  acid,  propionic  acid,  by  substituting 
a  halogen  atom  or  a  hydroxyl  group  for  hydrogen,  and  then 
employing  the  reactions  used  for  making  the  unsaturated  hydro- 
carbons from  similar  substitution  products  (p.  45) : 

CH2LCH2.CO.OH  +  KOH  =  CH2  :CH.CO.OH  +  KI  +  H2O. 
CH2OH.CH2.CO.OH  -  H2O  =  CH2:CH.CO.OH 

In  the  first  reaction  the  potassium  hydroxide  must  be  used  in 
alcoholic  solution ;  the  second  occurs  on  distillation.     Since  the 
1  See  Journal  of  American  Chemical  Society,  XXV,  511. 


Ill  SIMPLE   MONOBASIC   ACIDS 

corresponding  nitrile,  CH2:CH.CN,  does  not  exist,  the  general 
reaction  for  making  acids  from  their  nitriles  cannot  be  employed 
in  this  case. 

Acrylic  acid  is  not  unlike  acetic  acid  in  many  of  its  properties, 
but  it  gives  the  reactions  which  are  characteristic  of  an  unsatu- 
rated  compound,  uniting  directly  with  chlorine  and  bromine, 
with  halogen  acids,  and  with  hydrogen  (nascent)  to  form  saturated 
compounds.  When  oxidized,  it  breaks  at  the  double  bond.  The 
structural  formula  given  it  is  based  on  a  study  of  the  methods  of 
its  formation  and  its  reactions. 

Crotonic  acids,  C3H6CO.OH.  Four  acids  of  this  formula  are 
known,  two  of  which  have  a  special  theoretical  interest,  since 
they  have  the  same  constitutional  formula,  and  yet  differ  widely 
in  their  physical  characteristics. 

Crotonic  acid  (first  obtained  from  croton  oil)  is  a  solid,  melting 
at  72°  and  boiling  at  181°,  and  resembles  acrylic  acid  in  its  general 
behavior.  Isocrotonic  acid  is  an  oily  liquid  boiling  at  172°,  with 
an  odor  which  recalls  that  of  butyric  acid.  Both  acids  are 
present  in  crude  wood  vinegar  and  both  can  be  made  synthet- 
ically. Both  can  be  converted  into  butyric  acid  by  addition  of 
hydrogen  halides  followed  by  reduction  with  nascent  hydrogen; 
and  isocrotonic  acid  is  transformed  into  cro tonic  acid  by  continued 
heating  to  170-180°.  The  constitutional  formula  given  to  these 
acids  is  CH3.CH:CH.CO.OH,  and  the  differences  in  the  two 
acids  is  explained  as  the  result  of  so-called  geometrical  isomerism 
which  will  be  discussed  later  (p.  186). 

Propiolic  acid,  CHiC.CO.OH,  is  an  illustration  of  a  small 
group  of  acids  which  have  a  triple  bond.  It  is  related  to  propargyl 
alcohol  (p.  69)  as  acetic  acid  is  to  ethyl  alcohol,  but  cannot  be 
made  from  this  by  oxidation.  It  is  a  liquid.  When  cooled  it 
freezes,  and  the  crystalline  solid  melts  at  6°.  It  is  partly  de- 
composed when  distilled  under  ordinary  pressure,  but  distils 
unchanged  in  a  partial  vacuum.  It  unites  the  properties  of  an 
organic  acid  with  those  which  are  characteristic  of  acetylene,  and 
in  every  way  justifies  the  structural  formula  given  it. 


INTRODUCTION  TO   ORGANIC   CHEMISTRY  112 

Acids  with  Two  or  More  Double  Bonds.  —  Very  few  acids  of 
these  classes  are  known.  An  acid  with  two  double  bonds  is 
sorbic  acid,  CH3.CH:CH.CH:CH.CO.OH,  which  is  found  in  the 
unripe  berries  of  the  mountain  ash.  It  is  an  odorless,  crystalline 
solid,  melting  at  134.5°.  Linolic  acid,  CiyHsi.CO.OH,  whose 
glyceryl  ester  is  an  important  constituent  of  several  "drying  oils" 
(cf.  p.  i6oa),  has  also  probably  two  double  bonds.  Two  acids 
with  three  double  bonds  are  linolenic  and  isolinolenic  acids, 
CnH29.CO.OH,  whose  glyceryl  esters  are  in  linseed  oil. 

Further  Study  of  Oxidation 

We  have  learned  that  the  saturated  hydrocarbons  are  not 
oxidized  easily,  and  that  oxidation,  when  it  takes  place,  usually 
results  in  producing  the  end  products,  carbon  dioxide  and  water, 
without  such  intermediate  compounds  as  alcohols,  aldehydes, 
and  acids.  When,  however,  the  hydroxyl  group  is  present,  as 
in  alcohols,  oxidation  is  easily  effected  and  controlled,  so  that 
these  compounds  may  be  prepared. 

How  shall  we  picture  the  progress  of  these  oxidations?  When 
alcohol  is  oxidized  into  aldehyde,  the  net  result  is  the  removal  of 


two  atoms  of  hydrogen  from  the  primary  alcohol  group,  — 

OH 

with  the  formation  of  water  and  the  aldehyde  group,  —  CHO. 
The  first  suggestion  is  that  the  two  atoms  of  hydrogen  united 
to  the  carbon  atom  have  been  simply  burned  out  of  the  group. 
This,  however,  would  leave  =  C  —  O  —  H,  a  group  still  contain- 

O 
ing  hydroxyl,  while  in  the  aldehyde  group,   —  C<?      ,  the  hy- 

H 

drogen  and  oxygen  are  both  united  directly  with  a  saturated 
carbon  atom.  An  explanation  is  found  in  the  view  that  the 
first  action  of  the  oxygen  is  to  form  an  additional  hydroxyl  group: 

/OH 
-  CH2OH  +  O  =  -  CH< 


L\ 


OH 


113  SIMPLE   MONOBASIC  ACIDS 

and  that  this  arrangement,  being  unstable,  breaks  down  at  once 
into 

-  C  =  O  +  H20 


This  view  of  the  "mechanism"  of  oxidation  gains  force 
from  the  fact  that,  while  very  few  compounds  with  two  hydroxyl 
groups  united  to  the  same  carbon  atom  are  known,  the  compound 
whose  structural  formula  is 

/OH 
CC13.CH< 

X3H 

(chloral  hydrate)  is  a  well  known  and  comparatively  stable  sub- 

X)CH3 

stance;  and  a  number  of  compounds  of  the  type  CH3CH\  , 

X)CH8 

the  acetals,  are  known,  in  which  alkyl  groups  are  in  the  place  of 
the  hydrogen  of  the  double  hydroxyl  compound.     According  to 
this  view,  the  formation  of  a  ketone  from  a  secondary  alcohol 
would  involve  the  reactions: 
CH3.CH.OH.CH3  +  O  ->  CH3.C(OH)2CH3  -» 

CH3.CO.CH3  +  H2O 

while  the  oxidation  of  an  aldehyde  into  an  acid  evidently  consists 
simply  in  the  formation  of  a  hydroxyl  group  in  the  manner  just 
described: 

-CO.H  +  O  =  -CO.OH 

Further,  unsaturated  hydrocarbons,  which  are  readily  oxidized, 
yield  hydroxyl  derivatives.  This  is  the  view  of  the  course  of 
oxidation  which  is  generally  accepted,  and  it  is  applicable  to  all 
oxidations  of  organic  substances.  We  may  sum  the  matter  up  as 
follows:  i.  Saturated  hydrocarbons  are  not  readily  oxidized 
except  into  the  end  products,  carbon  dioxide  and  water.  Un- 
saturated hydrocarbons,  on  the  contrary,  are  easily  oxidized  and 
give  hydroxyl  derivatives.  2.  Saturated  compounds  already 


INTRODUCTION    TO    ORGANIC    CHEMISTRY 

containing  oxygen  in  a  hydroxyl  group,  or  an  aldehyde  group,  are 
easily  oxidized,  and  the  oxidation  affects  first  the  hydrogen  atoms 
united  to  the  carbon  atom  already  in  combination  with  oxygen. 
3.  The  immediate  result  of  the  oxidation  is  the  formation  of 
hydroxyl  groups.  4.  If  two  hydroxyl  groups  are  united  to  a  single 
carbon  atom,  the  system  is  unstable,  and  breaks  down  into 
oxygen,  which  remains  combined  with  the  carbon  by  both  valen- 
cies, and  water. 


CHAPTER  IX 
ACID  CHLORIDES;  ANHYDRIDES;  ESTERS 

Acyl  Chlorides 

When  phosphorus  trichloride  is  mixed  with  glacial  acetic  acid 
and  the  mixture  gently  heated,  hydrogen  chloride  is  copiously 
evolved,  and  on  distillation  of  the  remaining  liquid  a  compound 
is  obtained  which  boils  at  51°  and  has  the  molecular  formula, 
C2H3OC1.  It  reacts  readily  with  water,  forming  acetic  and 
hydrochloric  acids.  It  appears  from  these  reactions  that  the 
hydroxyl  group  of  acetic  acid  is  replaced  by  chlorine,  and  then 
restored;  so  that  the  structure  of  the  compound  first  formed  is 
CH3.CO.C1.  This  is  acetyl  chloride— the  group,  CH3.CO 
being  named  the  acetyl  group.  With  the  exception  of  formic  acid, 
similar  compounds  can  be  obtained  from  all  organic  acids,  and 
are  called,  generally,  acyl  chlorides,  acyl  being  a  general  name  for 
the  organic  acid  radical  or  group,  CnH2n+iCO.  All  attempts 
to  make  formyl  chloride  have  failed,  as  it  breaks  up  at  once  into 
carbon  monoxide  and  hydrogen  chloride: 

HCO.C1  =  CO  +  HC1. 

The  general  formula  for  the  acid  chlorides  of  the  acetic  acid 
series  is  CnH2n+iCO.Cl. 

Preparation. — i.  The  reaction  by  which  acetyl  chloride  is 
prepared,  as  above,  is: 

3CH3.CO.OH  +  2PC13  =  3CH3.CO.C1  +  3HC1  +  P2O3. 

2.  Phosphorus  pentachloride  gives  the  same  product  together 
with  phosphorus  oxy  chloride: 

CH3.CO.OH  +  PC15  =  CH3.CO.C1  +  POC13  +  HC1. 
114 


ACID  CHLORIDES;  ANHYDRIDES;  ESTERS  115 

These  are  general  reactions  for  making  the  acid  chlorides. 
For  the  lower  members  of  the  acetic  acid  series  the  reaction  with 
phosphorus  trichloride  is  preferred,  since  it  avoids  the  formation 
of  the  phosphorus  oxychloride  (boiling  point  107°)  from  which 
the  acyl  chloride  is  separated  with  some  trouble. 

Other  general  reactions  for  the  formation  of  acid  chlorides  are 
the  following:  3.  By  the  action  of  phosphorus  chlorides  or  oxy- 
chloride on  the  sodium  salts  of  the  acids,  and  4.  By  withdrawal 
of  the  elements  of  water  from  a  mixture  of  the  acid  and  hydro- 
gen chloride,  which  is  effected  by  leading  hydrogen  chloride  into 
a  mixture  of  the  acid  and  phosphorus  pentoxide: 


CH3.CO.OH  +  HC1  =  CH3.CO.C1  +  H2O 

In  the  commercial  preparation  of  acetyl  chloride  (for  laboratory 
use)  a  mixture  of  sulphur  dioxide  and  chlorine  is  passed  over  an- 
hydrous sodium  acetate.  Sulphuryl  chloride,  SO2C12,  appears 
to  be  first  formed,  and  this  reacts  with  the  acetate  as  follows: 

2CH3.CO.ONa  +  S02C12  =  2CH3.CO.C1  +  Na2SO4 

Properties  and  Reactions.  —  The  lower  members  of  the  series  are 
liquids  of  penetrating  odor,  which  fume  in  the  air,  because  of  the 
hydrogen  chloride  formed  by  the  aqueous  vapor  present.  The 
boiling  points  of  the  acyl  chlorides  are  lower  than  those  of  the  cor- 
responding acids,  an  effect  of  the  substitution  of  chlorine  for 
hydroxyl  like  that  found  in  the  boiling  points  of  alcohols  and  the 
corresponding  alkyl  chlorides.  The  acyl  chlorides  react  readily 
with  hydroxyl  and  amido  compounds,  and  acetyl  chloride  is  fre- 
quently employed  as  an  organic  reagent  (cf.  pp.  124,  138,  329,  etc.). 

i.  The  acyl  chlorides  are  insoluble,  as  such,  in  water,  but  are 
decomposed  by  it  with  the  formation  of  the  organic  acid  and  hydro- 
chloric acid: 

CHa.CO.Cl  +  H2O  =  CH3.CO.OH  +  HC1 


Il6  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

This  reaction  occurs  very  readily  and  violently  in  cold  water  with 
acetyl  chloride  and  a  few  of  the  next  higher  homologues,  but  more 
slowly  as  the  molecular  weight  increases.  Similar  reactions  take 
place  with  other  hydroxyl  compounds. 

2.  With  sodium  hydroxide  the  acetate  and  chloride  of  sodium 
are  formed. 

3.  With  alcohols,  an  ester  and  hydrogen  chloride  are  formed1, 

CHa.CO.Cl  +  C2H6OH  =  CH3.CO.OC2H6  +  HC1 

This  reaction  with  acetyl  chloride  is  a  valuable  one  for  determin- 
ing whether  a  compound  contains  the  hydroxyl  group  of  an  alcohol. 
The  facility  with  which  these  reactions  of  the  acyl  chlorides 
with  water  and  alcohols  take  place  stands  in  sharp  contrast  with 
the  behavior  of  the  alkyl  chlorides. 

4.  With  organic  acids  a  reaction  occurs  which  is  slow  and 
incomplete,  but  their  salts  react  readily  with  the  formation  of 
simple  or  mixed  acid  anhydrides  (p.  117): 

CH3.CO.C1  +  CH3.CO.OK  =  (CH3CO)2O  +  KC1 

5.  With  ammonia  the  acid  chloride  reacts  easily  with  the  for- 
mation of  acid  amides  (p.  137),  and  similar  reactions  occur  with 
substituted  ammonias,  such  as  aniline: 

CHa.CO.Cl  +  NH3  =  CH3.CO.NH2  +  HC1 

The  acyl  chlorides,  unlike  the  alkyl  chlorides,  do  not  react 
directly  with  sodium  or  other  metals. 

The  acid  bromides  and  iodides  are  of  much  less  importance 
than  the  chlorides.  The  bromides  are  sometimes  used  in  pre- 
paring bromine  substituted  acids,  as  a-brompropionic  acid, 
CH3.CH.Br.CO.OH,  since  replacement  by  bromine  occurs  more 
readily  in  the  acid  bromide  than  in  the  acid.  They  can  be  made 
by  the  action  of  the  phosphorus  bromide  (red  phosphorus  and 
bromine)  on  the  acids  or  their  salts. 


ACID  CHLORIDES;  ANHYDRIDES;  ESTERS 


117 


ACID  CHLORIDES  AND  ANHYDRIDES 


Name  of 

Formula      ACID  CHLORIDE  :  RC1             ACID  AN 

Acid 

of  Radical 

Melting 

Boiling                     Melti 

Point 

Point                       Poin 

Acetic 

CH3.CO 

51° 

Propionic 

C2H6.CO 

78 

Butyric  (norm.) 

C3H7.CO 

101 

Butyric  (iso) 

C3H7.CO 

92 

Valeric  (iso) 

C4H9.CO 

"5 

Heptylic 

C6H13.CO 

Caprylic 

C7H15.CO 

83 

Pelargonic 

C8H17.CO 

98 

«  "•          5° 

Capric 

C9H19.CO 

114 

IB 

Palmitic 

Ci5H31.CO 

12° 

192-5 

33         64 

Stearic 

Ci7H35.CO 

23 

215 

Boiling 
Point 

136° 
I67 
I92 
182 
215 
268-271 


Acid  Anhydrides 

We  have  seen  that  by  the  action  of  acetyl  chloride  on  sodium 
acetate  a  compound  is  produced  with  the  formula  (CHs.CO^O. 
This  is  the  anhydride  of  acetic  acid,  which  may  be  regarded  as  two 
acid  radicals  united  by  oxygen,  and  derived  from  two  molecules  of 
the  acid  by  the  withdrawal  of  the  elements  of  water.  It  corre- 
sponds, therefore,  to  the  inorganic  anhydrides,  SO  3,  ^Os,  etc. 
This  view  of  its  constitution  follows  immediately  from  the  method 
of  its  formation,  since  we  know  the  structure  of  the  acid  chloride 
and  of  the  sodium  acetate.  In  confirmation  of  this  formula  is  the 
fact  that  it  is  formed  (though  not  readily  and  only  in  small 
amounts)  by  the  action  of  phosphorus  pentoxide  on  glacial  acetic 
acid: 

2CH3.CO.OH  +  P2O5  =  (CH3.CO)2O  +  2HPO3 

Similar  compounds  are  obtained  corresponding  to  the  other 
acids  of  this  series,  except  in  the  case  of  formic  acid.  Formic  anhy- 
dride (HCO)2O,  like  its  chloride,  is  too  unstable  to  exist. 

Formation. — In  addition  to  the  methods  already  given,  the 
anhydrides  can  be  formed  by  the  action  of  the  acid  chlorides  OP 


Il8  INTRODUCTION  TO   ORGANIC  CHEMISTRY 

the  anhydrous  acids;  but  the  reaction,  like  that  of  the  direct  with- 
drawal of  water  from  the  acid,  is  slow  and  incomplete.  The  anhy- 
drides can  also  be  formed  from  the  salts  of  the  acids  by  heating 
them  with  carbonyl  chloride: 

2CH3.CO.ONa  +  COC12  =  (CH3CO)2O  +  C02  +  2NaCl 

They  are  almost  always  prepared,  however,  by  the  interaction  of 
the  sodium  salt  of  the  acid  and  its  chloride. 

Properties. — Acetic  anhydride,  or  acetyl  oxide,  and  its  next 
homologues  are  liquids  whose  boiling  points  are  higher  than  those 
of  the  acids  from  which  they  are  derived.  The  anhydrides  of 
greater  molecular  weight  are  solids.  They  are  all  insoluble  in 
water,  but  soluble  in  ether.  Acetic  anhydride  is  the  most  impor- 
tant of  this  group. 

Reactions. — The  anhydrides  react  with  hydroxyl  compounds  in 
a  manner  similar  to  the  acid  chlorides,  but  less  vigorously,  and,  like 
the  chlorides,  they  are  much  used  to  identify  the  alcoholic 
hydroxyl  group. 

1.  Like  the  inorganic  anhydrides,  the  organic  anhydrides  are 
converted  into  acids  by  water.     The  reaction,  however,  even  with 
acetic  anhydride,  is  very  slow  in  cold  water;  and  some  of  the 
higher  anhydrides  can  be  boiled  in  water  for  a  considerable  time 
without  being  completely  changed.     With  solutions  of  alkalies 
the  reaction  takes  place  easily  with  the  formation  of  the  salt  of  the 
acid. 

2.  With  alcohols,  the  anhydrides  give  an  ester  and  the  acid: 

(CH3.CO)2O  +  C2H5OH  =  CH3.CO.OC2H5  +  CH3.CO.OH 

3.  With  organic  acids,  the  anhydrides  act  only  when  heated, 
and  then  slowly.     This  reaction  gives  a  method  for  making  mixed 
anhydrides,  for  instance,  with  propionic  acid: 

CH3.CO\ 
(CH3.CO)2O  +  C2H5.CO.pH  =  yo  +  CH3.CO.OH 

Acetic  anhydride  Propionic  acid          C2Hs.CC) 


ACID  CHLORIDES;  ANHYDRIDES;  ESTERS  119 

Such  mixed  anhydrides  are  decomposed  by  distillation  into  the 
simple  anhydrides. 

4.  With  hydrochloric  acid,  a  reaction  of  the  same  kind  occurs: 

(CH3.CO)2O  +  HC1  =  CH3.CO.C1  +  CH3.CO.OH 

Acetyl  chloride  may  be  thus  regarded  as  a  mixed  anhydride  of 
acetic  and  hydrochloric  acids. 

5.  With  ammonia,  acid  amides  are  formed: 

(CH3.CO)2O  +  2NH3  =  2CH3CO.NH2  +  H2O 

Acetamide 

6.  Chlorine  and  bromine  act  very  readily  on  the  anhydrides, 
substituting  for  one  hydrogen  atom,  while  the  hydrogen  halide 
which  is  formed  reacts  on  the  substituted  anhydride,  so  that  the 
final  products  are  the  acyl  halide,  and  the  monohalogen  substi- 
tuted acid;  e.g.,  CH3.CO.C1  and  CH2C1.CO.OH. 

7.  Nascent  hydrogen  (sodium  amalgam)  reduces  anhydrides 
to  aldehydes  and  alcohols,  but  the  reaction  yields  other  products 
as  well. 

The  student  should  compare  the  reactions  of  the  anhydrides 
with  those  of  the  acyl  halides  (and  esters)  and  decide  how  an 
anhydride  may  be  identified. 

Esters  of  Inorganic  Acids 

Both  inorganic  and  organic  acids  react  with  alcohol  with  the 
formation  of  compounds  which  are  called  esters. 

Esters  of  Sulphuric  Acid. — When  concentrated  sulphuric  acid 
is  mixed  with  ethyl  alcohol  and  the  mixture  heated  for  some  time 
on  a  water  bath,  an  acid  compound  is  formed  which  gives  with 
barium  carbonate  a  soluble  barium  salt,  and  thus  may  be  sepa- 
rated from  any  unchanged  sulphuric  acid.  If  just  enough  sul- 
phuric acid  is  added  to  the  solution  of  this  barium  salt  to  exactly 
precipitate  the  barium,  there  is  obtained,  on  evaporation  of  the 


120  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

filtrate,  a  thick  acid  liquid  which  cannot  be  distilled  without 
decomposition  into  ethylene  and  sulphuric  acid.  Most  of  the 
salts  of  this  acid  compound  are  soluble  in  water  and  can  be 
obtained  pure  by  crystallization.  Analysis  of  these  salts  shows 
that  they  may  be  regarded  as  derived  from  an  acid  whose  composi- 
tion is  H(C2H5)SO4,  ethyl  hydrogen  sulphate.  The  normal  ethyl 
sulphate  or  diethyl  sulphate,  may  be  made  by  the  reactions  of 
silver  sulphate  and  ethyl  iodide: 

Ag2S04  +  2C2H5I  =  (C2H5)2S04  +  2AgI 

This  reaction  gives  conclusive  evidence  as  to  the  structure  of  this 
compound. 

It  is  a  liquid  of  pleasant  peppermint-like  odor,  which  boils  at 
208°  with  only  slight  decomposition. 

Ethyl  hydrogen  sulphate,  or  ethyl  sulphuric  acid,  is  an  interme- 
diate product  in  the  reactions  by  which  ethylene  and  ether  are 
prepared  (pp.  46  and  70).  Although  the  final  result  of  these 
reactions  may  be  expressed  as  due  to  the  withdrawal  of  the 
elements  of  water  from  one  or  from  two  molecules  of  alcohol,  the 
actual  progress  of  the  reactions  is  represented  by  the  following 
equations. 

For  ethylene: 

C2H5OH  +  H2SO4  *=*  H(C2H5)SO4  +  H2O 
and  H(C2H5)SO4  =  CH2 :  CH2  +  H2SO4 

In  the  ether  formation,  ethyl  sulphuric  acid  is  formed  as  above, 
and  then  reacts  with  another  molecule  of  alcohol: 

H(C2H5)S04  +  C2H5OH  =  (C2H5)20  +  H2SO4 

The  course  of  the  principal  reaction  is  determined,  as  has  been 
stated,  by  the  proportions  of  acid  and  alcohol  which  are  used,  and 
the  temperature. 

Ethyl  sulphuric  acid  is  also  formed  when  ethylene  is  led  into  the 
concentrated  acid.  This  gives  an  interesting  method  for  making 


ACID  CHLORIDES;  ANHYDRIDES;  ESTERS  121 

ethyl  alcohol  from  inorganic  materials.  For  from  calcium  car- 
bide (lime  and  coke),  acetylene  is  obtained  by  the  action  of  water, 
and  acetylene  is  readily  converted  into  ethylene  by  hydrogen  in 
the  presence  of  platinum  black. 

When  heated  with  water,  ethyl  sulphuric  acid  is  converted  into 
alcohol  and  sulphuric  acid: 

H(C2H5)S04  +  H2O  +±  C2H5OH  +  H2SO4 

Ethyl  sulphuric  acid  or  its  salts  are  frequently  used  in  preparing 
other  ethyl  compounds  by  such  reactions  as: 

K(C2H5)SO4  +  KBr  =  C2H6Br  +  K2SO4 
K(C2H5)SO4  +  KCN  =  C2H5CN  +  K2SO4 

Sulphuric  acid  esters  containing  other  alkyl  groups  may  be 
obtained  by  the  methods  given  for  making  the  ethyl  compounds, 
and  resemble  these  in  their  properties. 

Esters  of  Other  Inorganic  Acids. — The  hydrogen  of  other 
inorganic  acids  may  be  replaced  by  alkyl  groups  with  the  forma- 
tion of  esters.  These  esters  are  mostly  oily  liquids  which  are 
more  or  less  easily  hydrolyzed  into  alcohol  and  acid  by  water,  and 
are  in  all  cases  decomposed  by  boiling  solutions  of  alkalies  into 
alcohols  and  salts. 

The  normal  esters  are  insoluble  or  only  slightly  soluble  in  water, 
but  the  acid  esters  are  soluble;  an  illustration  of  the  influence  of 
the  presence  of  the  hydroxyl  group  on  solubility  in  water.  (Com- 
pounds containing  this  group  are  mostly  more  or  less  soluble  in 
water,  while  those  in  which  the  group  is  absent  are  usually  insol- 
uble or  nearly  insoluble.  Among  the  compounds  we  have  so  far 
considered  this  is  seen  to  be  true,  except  in  the  case  of  the  alde- 
hydes and  ketones.) 

In  the  formation  of  the  esters  by  the  direct  action  of  the  acids 
on  the  alcohols,  the  reaction  is  never  complete,  and  when  the  acid 
is  polybasic  an  acid  ester  (or  alkyl  acid)  is  formed.  The  best 


122  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

general  method  for  making  the  normal  esters  is  by  the  reaction 
between  the  silver  salt  of  the  acid  and  the  alkyl  halide  as  in  the  case 
of  ethyl  sulphate.  For  instance: 

Ag3As03  +  3C2H5I  =  (C2H5)3AsO3 


The  acid  esters  are,  as  a  rule,  less  stable  than  the  normal  ones. 
They  are  odorless  and  decompose  when  distilled.  Their  salts, 
however,  are  more  stable  than  the  esters  themselves. 

The  normal  esters  often  have  a  pleasant  fruity  odor,  and  can 
usually  be  distilled  without  decomposition. 

The  nitric  and  nitrous  esters  of  methyl  and  ethyl  are  readily 
hydrolyzed  to  acid  and  alcohol;  the  nitric  esters  are  converted 
by  nascent  hydrogen  (tin  and  hydrochloric  acid)  into  hydroxyl- 
amine  and  alcohol: 

C2H5ON02  +  6H  =  NH2OH  +  C2H5OH  +  H2O. 

Hydroxylamine 

The  nitric  ester  of  glycerol,  a  polyhydroxyl  alcohol,  is  de-: 
scribed  on  page  159. 

Ethyl  nitrite,  C2H5ONO  known  in  alcoholic  solution  as  "sweet 
spirit  of  nitre,"  and  isoamyl  nitrite  are  used  in  medicine. 

The  alkyl  halides  are  esters  of  the  halogen  acids,  but  on  account 
of  their  importance  in  various  reactions  and  the  fact  that  many  of 
them  can  be  made  directly  from  the  hydrocarbons  by  the  action 
of  halogens,  have  been  already  discussed  (p.  31). 

ESTERS 

Nitrite  Nitrate  Sulphate  Acetate 

B.p.  B.p.  (neutral)  B.p. 

B.p. 

Methyl  -12°  66°  187°                   57.3° 

Ethyl  17  87  208                     77.5 

Propyl  57  110.5  101.8 

Isopropyl  45  101  .  5  c.  90 

Butyl  (norm.)  75  .....  124.5 

Isobutyl  67  123  116.3 


ACID  CHLORIDES;  ANHYDRIDES;  ESTERS 


123 


Boiling 

Point 

Formic  acid 

55° 

Acetic 

77-5 

Propionic 

98.8 

Butyric  (norm.) 

120.9 

Butyric  (iso.) 

IIO.  I 

Valeric  (norm.) 

144.7 

Valeric  (iso.) 

134-3 

ETHYL  ESTERS 


Caproic 

Heptylic 

Caprylic 

Pelargonic 

Capric 

Palmitic 
Stearic 


Boiling  Point 

166.6° 
187.1 
205.8 
227-228 

243-245 
Melting  Point 

24° 

34-34 


Esters  of  Organic  Acids 

Ethyl  acetate,  which  makes  its  presence  known,  when  ethyl 
alcohol  and  acetic  acid  or  an  acetate  are  heated  with  sulphuric 
acid,  by  the  agreeable  fruity  odor  which  serves  as  a  test  for  the 
acetic  acid  radical,  is  a  typical  member  of  a  large  group  of  similar 
compounds.  Several  reactions  into  which  it  enters  have  already 
been  given  (pp.  35  and  99). 

It  is  formed  when  alcohol  and  acetic  acid  are  mixed  and  heated; 
but  the  reaction  goes  on  very  slowly  and,  as  it  is  rather  readily 
reversible,  an  equilibrium  is  established  far  short  of  completion. 
An  excess  of  either  acid  or  alcohol  causes  a  larger  proportion  of  the 
one  present  in  smaller  amount  to  be  changed  into  the  ester;  and 
in  the  presence  of  a  water- withdrawing  agent  the  conversion  may 
be  nearly  complete.  When  the  ester,  already  made,  is  mixed 
with  water  it  is  slowly  transformed  into  acid  and  alcohol.  The 
reaction  by  which  it  is  formed  appears,  thus,  to  consist  in  the 
separation  of  the  elements  of  water  from  acid  and  alcohol: 


CH3.CO.OH 

Acetic  acid 


C2H5OH 

Alcohol 


H2O 


CH3.CO.OC2H5 

Ethyl  acetate 


and  (since  the  formulas  of  the  acid  and  alcohol  are  known),  the 
formula  given  in  the  above  equation  for  the  ester  is  plainly  indi- 
cated. This  is  proved  to  be  the  right  formula  by  other  reactions 


124  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

in  which  the  ester  is  made  from  substances  with  known  formulas, 
as  from  acetic  acid  or  an  acetate  with  ethyl  halide,  or  from  acetyl 
chloride  with  sodium  ethoxide. 


CH3.CO.ONa  +  C2H5l  =  CH3.CO.OC2H6  +  Nal 
CH3.CO.C1  +  C2H5ONa  =  CH3.CO.OC2H6  +  NaCl 

In  the  usual  method  for  the  preparation  of  ethyl  acetate  from 
alcohol  and  acetic  acid  with  the  addition  of  sulphuric  acid,  ethyl 
sulphuric  acid  is  first  formed,  and  then  reacts  with  the  acetic 
acid: 


In  another  procedure  hydrogen  chloride  is  led  into  the  mixture  of 
acid  and  alcohol.  One  explanation  of  the  effect  of  the  hydrogen 
chloride  is  that  it  acts  as  a  water-withdrawing  substance,  while 
according  to  another  interpretation  of  the  reaction,  acetyl  chlo- 
ride is  an  intermediate  product  which  then  reacts  as  follows: 

CH3.CO.C1  +  C2H5OH  <=»  CH3.CO.OC2H5  +  HC1 

Ethyl  acetate  is  also  formed  from  alcohol  and  acetic  anhydride 
(p.  118). 

Properties  and  Reactions.  —  Ethyl  acetate  is  a  liquid  which  boils 
at  77°  and  is  soluble  in  about  17  parts  water.  It  enters  readily 
into  a  number  of  reactions. 

1.  With  water  it  is  partly  hydrolyzed.     The  hydrolysis  is 
aided  by  the  presence  of  a  small  amount  of  an  inorganic  acid  and 
boiling. 

2.  With  caustic  alkalies,  complete  decomposition  is  readily 
effected  with  the  production  of  alcohol  and  an  acetate: 

CH3.CO.OC2H5  +  NaOH  =  CH3.CO.ONa  +  C2H6OH 

This  reaction,  which  can  be  carried  out  with  all  esters,  is  called 
"  saponification  "  from  the  fact  that  soap  is  made  in  this  way  from 
fats,  which  are  esters  of  glycerol  (p.  160).  The  term  is  often 


ACID  CHLORIDES;  ANHYDRIDES;  ESTERS  125 

extended  to  the  decomposition  by  water,  in  which  no  salts  are 
produced,  and  the  saponification  process  is  often  termed  hydrolysis. 
The  rate  at  which  the  hydrolysis  proceeds  depends  on  the 
temperature  and  concentration  of  the  solution  as  well  as  on  the 
nature  of  the  hydrolyzing  agent  and  of  the  ester. 

3.  Concentrated  halogen  acids  when  heated  with  ethyl  acetate 
form  acetic  acid  and  ethyl  halide: 

CH3.CO.OC2H5  +  HC1  =  CH3.CO.OH  +  C2H5C1 

The  action  is  more  rapid  the  higher  the  molecular  weight  of  the 
acid;  thus  hydriodic  acid  acts  most  quickly  and  hydrofluoric 
acid  the  most  slowly. 

4.  Ammonia  converts  ethyl  acetate  into  acetamide  (p.  138): 

CH3.CO.OC2H5  +  NH3  =  CH3.CO.NH2  +  C2H6OH 

Acetamide 

Other  esters  of  organic  acids  may  be  made  by  the  methods  used 
for  ethyl  acetate,  and  their  reactions  are  of  the  same  kind.  Many 
organic  esters  are  found  in  nature,  and  a  considerable  number  are 
manufactured  as  artificial  fruit  essences.  Isoamyl  acetate  has  the 
odor  of  pears;  octyl  acetate ,  that  of  oranges;  ethyl  butyrate,  that  of 
pineapples;  isoamyl  isovaleriate  that  of  apples,  etc.  The  natural 
fats,  as  we  have  seen  (p.  108),  are  esters  of  glycerol,  and  various 
waxes  are  composed  chiefly  of  esters  of  the  higher  homologues  of 
acetic  acid  and  the  higher  alcohols.  Spermaceti  is  mostly  cetyl 
palmitate;  beeswax  contains  myricyl  palmitate;  etc.  (See  also 
p.  160.) 

Esters  of  both  inorganic  and  organic  acids  are  named  as  alkyl 
salts  of  the  acids,  and  sometimes  called  ethereal  salts.  Most  of 
their  reactions  are  analogous  to  those  of  inorganic  salts  formed 
from  weak  bases  and  weak  acids,  and  which  are  readily  hydrolyzed. 
There  is,  however,  this  difference,  that  the  hydrolysis  of  the  salts 
takes  place  quickly,  while  that  of  the  esters  is  slow.  In  other 
words,  the  esters  are  ionized  very  slightly,  while  the  salts  are  usu- 
ally more  or  less  highly  ionized. 

The  rate  at  which  esters  are  formed  from  the  alcohol  and  the 


126  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

acid,  and  the  progress  of  their  hydrolysis  are  both  so  slow  that 
these  processes  have  proved  very  valuable  to  theoretical  chemistry . 
Their  quantitative  study  has  given  information  as  to  the  influence 
of  different  conditions  on  the  velocity  of  reactions:  such  as  the 
effect  of  mass  or  molecular  concentration,  of  temperature,  and  of 
ionic  concentration  (influence  of  acids  and  bases  on  hydrolysis). 

In  the  esters  of  organic  acids  two  carbon  atoms  are  united  by 
oxygen.  We  find  a  similar  linkage  in  the  ethers  and  in  the  acid 
anhydrides.  In  the  ethers  two  alkyl  groups  are  linked,  in  the 
anhydrides  two  acyl  groups.  In  the  esters  the  two  groups  held 
together  by  oxygen  are  an  alkyl  and  an  acyl  group,  and  we  find 
in  comparing  the  reactions  of  these  three  classes  of  compounds 
that  the  esters  are  in  some  respects  intermediate  between  the 
ethers  and  the  anhydrides. 


CHAPTER  X 
AMINES  AND  AMIDES.    NITRO -COMPOUNDS 

In  several  reactions  which  we  have  studied,  ammonia  has  been 
represented  as  acting  in  such  a.  way  as  to  produce  compounds 
containing  the  group  NH2.  When  this  group  is  united  to  an 
alkyl  radical,  as  in  CH3.NH2,  the  compound  is  called  an  amine; 
when  combined  with  an  acyl  radical,  as  in  CH3.CO.NH2,  an 
amide.  The  group  NH2  itself  receives  a  correspondingly  different 
name  in  the  two  classes  of  compounds,  being  termed  the  amino 
group  in  amines,  and  the  amido  group  in  amides.  Both  amines 
and  the  amides  may  be  regarded  as  substituted  ammonias,  and 
their  behavior,  especially  that  of  the  amines,  abundantly  justifies 
this  view. 

There  are,  also,  related  compounds  in  which  two  or  all  three 
hydrogen  atoms  of  the  ammonia  molecule  are  replaced  by  alkyl  or 
acyl  radicals;  and  the  three  classes  of  substituted  ammonias  are 
distinguished  by  the  names  of  primary,  secondary,  and  tertiary, 
according  as  one,  two, or  three  hydrogen  atoms  have  been  replaced. 

The  Amines 

The  amines  show  their  relationship  to  ammonia  by  combining 
directly  and  additively  with  acids  to  form  salts  which  are  like 
the  ammonium  salts,  and  from  which  the  amines  are  liberated  by 
alkalies,  just  as  ammonia  is  from  ammonium  salts. 

Formation. — i.  By  the  action  of  ammonia  in  alcoholic  solution 
on  alkyl  halides.  This  reaction  does  not  take  place  readily, 
requiring  a  temperature  which  can  be  attained  with  these  volatile 

127 


128  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

substances  only  by  heating  them  in  sealed  tubes.  The  product 
is  a  mixture  of  the  three  classes  of  amines  together  with  quaternary 
compounds  which  are  completely  substituted  ammonium  halides. 
The  reactions  for  the  methyl  compounds  are: 

*NH3  +  CH3I  =  CH3NH2.HI 
CH3NH2.HI  +  GH3I  =  (CH3)2NH.HI  +  HI 
(CH3)2NH.HI  +  CH3I  =  (CH3)3N.HI  +  HI 
(CH3)3N.HI  +  CH3I  =  (CH3)4N.I  +  HI 


The  formation  of  a  single  product  cannot  be  assured  by  using 
definite  proportions  of  ammonia  and  the  alkyl  halide,  and  the 
amounts  of  the  four  compounds  which  are  produced  depend  on 
the  nature  of  the  alkyl  group. 

The  alkyl  ammonium  salts,  with  the  exception  of  the  tetra- 
amine  salt,  are  all  decomposed  by  caustic  alkalies,  yielding 
ammonia-like  amines;  in  the  cases  taken  for  illustration,  CH3.NH2, 
(CH3)2NH,  and  (OH,),**. 

The  mixture  of  amines,  obtained  by  distillation  of  the  salts 
with  caustic  alkali,  is  separated  with  some  difficulty.  Fractional 
distillation  is  not  usually  successful,  and  no  entirely  satisfactory 
general  method  can  be  given.  When  dealing  with  considerable 
quantities,  the  following  procedure  is  often  employed  for  the 
methyl  and  the  ethyl  amines:  The  greater  part  of  the  primary 
amine  is  obtained  as  chloride  or  oxalate  by  fractional  crystalliza- 
tion of  these  salts.  Then  by  the  action  of  nitrous  acid  on  the 
residue,  the  remaining  amount  of  primary  amine  is  decomposed 
into  alcohol,  water,  and  nitrogen,  while  the  tertiary  amine  is 
unchanged;  and  the  secondary  amine  is  converted  in  to  a  nitroso- 
amine  (p.  131)  which  is  an  oil  and  readily  separated  from  the 
unaltered  tertiary  amine.  Finally  from  the  nitroso-amine  the 
secondary  amine  in  the  form  of  its  chloride  is  obtained  pure  by 
treatment  with  concentrated  hydrochloric  acid. 

Other  Methods  for  Making  the  Amines.  —  Among  the  other  meth- 


AMINES   AND   AMIDES;   NITRO-COMPOUNDS  1 29 

ods  by  which  primary  amines  can  be  formed,  the  following  are  the 
more  important. 

2.  By  treating  an  ester  of  isocyanic  acid  (p.  154)  with  potassium 
hydroxide: 

C2H5.N:C:0  +  2KOH  =  C2H5NH2  +  K2CO3. 

This  method  is  of  especial  interest  as  it  is  the  one  by  which  the 
first  amine  was  discovered  (Wurtz,  1848).  The  resulting  gaseous 
amine  was  believed  to  be  ammonia  until,  by  chance,  it  was  found 
to  be  inflammable. 

3.  From  amides   (p.    1*37),  by  treatment  with  bromine  and 
sodium  hydroxide  (or  sodium  hypobromite) ;  Hofmanri's  reaction.*/ 
The  reaction,  whose  net  result  is  the  removal  of  CO  from  the 
acetamide,  proceeds  by  the  following  steps: 

CH3.CO.NH2  +  Br2  +  NaOH  =  CH3.CO.NHBr  +  NaBr  +  H2O 
CH3.CO.NHBr  +  NaOH  =  CH3.N:C:O  +  NaBr  +  H2O 
CH3.N:C:O  +  2NaOH  =   CH3.NH2  +  Na2CO3. 

The  last  step  in  this  method  is  the  Wurtz  reaction  given  above  (2). 

This  reaction  furnishes  a  means  of  "building  down"  from  higher 

to  lower  hydrocarbon  derivatives.     For  instance,  starting  with 

propyl  alcohol,  ethyl  alcohol  may  be  made  by  the  following  steps: 

CH3.CH2.CH2.OH  -»  CH3.CH2.CO.OH  -> 

CH3.CH2.CO.NH2  ->  CH3.CH2.NH2  ->  CH3.CH2.OH. 

The  last  step  is  effected  by  decomposition  of  the  amine  nitrite 
(p.  131).  (Compare  this  method  of  going  from  one  compound 
to  another  with  a  less  number  of  carbon  atoms  with  the  formation 
of  hydrocarbons  from  the  salts  of  the  higher  acids.) 

4.  By  reduction  of  various  nitrogen  compounds — nitro-com- 
pounds,  alkyl     cyanides,  oximes,  and  hydrazones.     From  the 
alkyl  cyanide  (nitrile),  for  example,  by  "nascent"  hydrogen: 

CH3.CN  +  4H  =  CH3.CH2.NH2 
This  is  best  effected  by  the  action  of  sodium  in  alcoholic  solution. 


130  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

Since  the  formation  of  an  alkyl  cyanide  adds  an  atom  of  carbon 
to  the  original  compound,  its  conversion  into  an  amine  may  be 
employed  as  a  means  of  passing  from  one  alcohol  to  the  next 
higher  in  the  series.  For  instance,  CH3OH  -»  CH3I  —>  CH3.- 
CN->  CH3.CH2NH2  -»  CH3.CH2OH.  The  last  step  is  effected 
by  the  decomposition  of  the  amine  with  nitrous  acid. 

5.  From  alkyl  esters  of  inorganic  acids  by  the  action  of  am- 
monia. The  reaction  with  the  esters  of  the  halogen  acids  (alkyl 
halides)  has  already  been  discussed.  The  nitric  and  sulphuric 
acid  esters  react  in  a  similar  manner.  The  action  of  ammonia  on 
the  esters  of  organic  acids  produces  acid  amides  and  alcohol. 

In  spite  of  the  numerous  methods  for  forming  amines,  there  is  no 
way  by  which  the  pure  substances  may  be  easily  prepared  in  any 
quantity. 

Properties. — The  primary,  secondary,  and  tertiary  methyl 
amines,  and  primary  ethyl  amine  are  gases  at  ordinary  tempera- 
tures. The  amines  of  higher  molecular  weight  are  liquid  and  fi- 
nally solid.  The  lower  amines  have  odors  unpleasantly  resembling 
that  of  ammonia,  and  are  freely  soluble  in  water.  The  odor 
grows  less  and  the  solubility  decreases  with  an  increase  in  the 
number  of  the  carbon  atoms,  and  the  highest  amines  are  odorless 
and  insoluble.  They  are  all  lighter  than  water.  The  solutions  of 
the  lower  amines  are  strongly  alkaline,  and  like  that  of  ammonia 
probably  contain  the  unstable  hydroxides  of  the  alkyl  ammoniums. 
The  ionization  of  these  hydroxides  is  shown  by  their  alkaline  reac- 
tion, by  the  precipitation  of  hydroxides  of  metals  from  their  salt 
solutions,  and  by  the  readiness  with  which  they  form  ammonium- 
like  salts.  Their  electrical  conductivity  indicates  that  the  lower 
amine  hydroxides  are  more  highly  dissociated  than  ammonium 
hydroxide,  the  bacisity  being  least  in  the  tertiary,  and  greatest 
in  the  secondary  amines  (cf.  p.  410). 

The  halide  salts  of  amines  are  soluble  in  alcohol  and  may  be 
thus  separated  from  ammonium  halides  which  are  insoluble. 
Like  ammonium  chloride,  however,  the  amine  chlorides  form  dou- 


AMINES  AND  AMIDES;   NITROCOMPOUNDS  131 

ble  salts  with  platinum. chloride,  which  are  sparingly  soluble  in 
alcohol.  Methyl  and  ethyl  amines  differ  from  ammonia  most 
markedly  by  their  inflammability;  and  their  hydroxides,  unlike 
solutions  of  ammonia,  dissolve  aluminium  hydroxide. 

Reactions. — i.  On  oxidation  of  the  amines,  the  alkyl  groups 
are  split  off  and  converted  into  the  corresponding  aldehydes 
or  acids. 

The  other  reactions  of  the  amines  differ  with  the  number  of 
alkyl  groups  they  contain.  The  tertiary  amines  are  rather  indif- 
ferent to  reagents,  while  the  primary  amines  are  more  readily 
acted  on  than  the  secondary. 

2.  An  important  reaction  which  serves  to  distinguish  the  three 
classes  is  that  with  nitrous  acid.  A  primary  amine  in  acid  solu- 
tion, when  warmed  with  sodium  nitrite,  decomposes  with  the  pro- 
duction of  nitrogen,  alcohol,  and  water: 

C2H5.NH2  -h  HNO2  =  N2  +  C2H6OH  +  H2O 

We  may  suppose  that  the  nitrite  of  the  amine,  C2H5NH2.HNO2, 
is  first  formed  and  then  decomposes  like  ammonium  nitrite,  where, 
however,  as  no  alkyl  group  is  present,  nitrogen  and  water,  instead 
of  alcohol  and  water,  are  formed: 

NH4NO2  =  N2  -f  HOH  -f  H2O 

On  secondary  amines,  nitrous  acid  acts  less  vigorously,  and  gives 
insoluble  nitroso-amines,  compounds  in  which  the  fiydrogen  of  the 
amine  is  replaced  by  the  nitroso-group — NO: 

(C2H5)2:NH  +  HONO  =  (C2H5)2:N.N:O  +  H2O 

When  a  nitroso-amine  is  treated  with  phenol  and  concentrated 
sulphuric  acid,  it  gives  a  dark  green  solution  which  becomes  red 
when  diluted  with  water,  and  with  an  excess  of  alkali  assumes  an 
intense  blue  or  green.  This  reaction  (Liebermann's)  serves  for 
the  detection  of  nitroso-amines  and  hence  of  secondary  amines. 

On  tertiary  amines,  nitrous  acid  hardly  acts  at  all,  and  if  action 


132  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

occurs  it  is  usually  with  the  production  of  oxidation  products  and 
oxides  of  nitrogen. 

Since  the  secondary  amines  can  be  recovered  from  their  nitroso- 
compounds  by  means  of  concentrated  hydrochloric  acid,  the  reac- 
tion gives  a  means  for  obtaining  them  from  mixtures  with  the 
other  two: 

(C2H5)2:N.N:O  +  2HC1  =  (C2H5)2:NH.HC1  +  NOC1 

3.  Primary  amines  give  a  characteristic  reaction  with  chloro- 
form and  caustic  alkali.     When  warmed  with  chloroform  and  an 
alcoholic  solution  of  potassium  hydroxide,  an  isocyanide  (formerly 
called  carbylamine)  is  formed  which  is  recognized  by  its  charac- 
teristic and  unendurable  odor  (carbylamine  reaction): 

C2H5.NH2  +  CHC13  +  3KOH  =  C2H6.NC  +  3KC1  +  3H2O. 

Ethyl 
isocyanide 

4.  With  both  primary  and  secondary  amines,  acetyl  chloride 
reacts  at  once  without  warming,  forming  compounds  by  the  with- 
drawal of  hydrogen  chloride.     With  tertiary  amines  no  reaction 
occurs. 

With  alkyl  halides,  primary  amines  combine  additively,  forming 
the  halide  salt  of  the  secondary  amine.  Secondary  amines,  in 
like  manner,  give  the  tertiary;  and  the  tertiary,  the  quaternary 
amine  salt. 

Some  Individual  Amines. — All  three  of  the  methyl  amines  occur 
in  herring  brine,  the  tertiary  amine  in  the  largest  proportion. 
They  are  all  gases.  The  primary  amine  has  an  odor  very  like  that  of 
ammonia,  but  with  a  fishy  suggestion.  In  the  secondary  and 
tertiary  amines  the  fishy  character  of  the  odor  becomes  very  pro- 
nounced. Monomethyl  amine  also  occurs  in  Mercurialis  perennis, 
and  is  one  of  the  products  of  the  destructive  distillation  of  wood, 
bones,  and  other  natural  substances.  Trimethyl  amine  is  found  in 
a  number  of  plants,  and  can  be  obtained  from  wine  by  dis- 
tilling with  caustic  alkali.  Commercial  "trimethyl  amine," 
obtained  as  a  product  of  the  dry  distillation  of  residues  left  after 


AMINES   AND    AMIDES;    NITRO-COMPOUNDS  133 

making  alcohol  from  beet-root  molasses,  is  chiefly  dimethyl  amine 
(50  per  cent.)  with  monomethyl  and  several  higher  amines,  and 
only  about  5  per  cent,  of  the  trimethyl  amine.  It  is  used  as  a 
source  of  methyl  chloride  and  ammonia: 

(CH3)3N  +  4HC1  =  3CH3C1  +  NH4C1 

The  best  method  for  the  laboratory  preparation  of  trimethyl 
amine  is  by  the  distillation  of  tetramethyl  amine  hydroxide 
(p.  135).  It  is  curious  that  trimethyl  amine,  which  has  a  most 
offensive  odor  when  diluted  with  other  gases,  is  almost  indistin- 
guishable from  ammonia  when  concentrated,, 

Hexamethylene  tetramine,  CeH^N^  formed  by  the  action  of 
ammonia  on  formaldehyde  (p.  84),  is  a  weakly  basic  crystalline 
substance  which  under  the  name  "  urotropin,"  and  in  the  form 
of  the  ethyl  bromide.  "  bromalin,"  and  of  the  salicylate,  "  sal- 
formin,"  has  found  some  use  in  medicine.  When  heated  with 
acids,  it  breaks  up  into  formaldehyde  and  ammonia,  some  methyl 
amine  being  formed  at  the  same  time.  Its  constitution  is  unknown. 


Vinyl  amine,  either  CH2  :CH.NH2  or         yNH,  is  often  cited 

CH/ 

as  an  unsaturated  amine;  but  as  it  does  not  decolorize  potassium 
permanganate  as  an  unsaturated  compound  should,  the  second, 
cyclic  formula,  is  the  more  probable  one.  The  amine  is  known 
only  in  its  strongly  alkaline  (hydroxide)  aqueous  solution  and  in 
its  salts.  It  is  made  from  bromethyl  amine,  CH2Br.CH2NH2, 
by  means  of  moist  silver  oxide  or  potassium  hydroxide.  It  com- 
bines with  sulphurous  acid  to  form  taurine,  CH2(SO3H).CH2NH2, 
which  in  combination  with  cholic  acid  is  the  chief  constituent  of 
bile. 

/CH:CH2 

Neurine,  (CH3)3N\  is   a  mixed   quaternary   amine 

XOH 

hydroxide  which  contains  the  vinyl  radical.  It  has  been  synthe- 
sized, and  is  a  substance  of  physiological  importance,  being 


134  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

formed  in  the  putrefaction  of  meat  and  in  other  fermentative  proc- 
esses. It  is  very  poisonous,  belonging  to  the  class  of  basic  com- 
pounds formed  in  the  decay  of  animal  substances  which  are 
known  as  ptomaines,  many  of  which  are  also  poisonous.  Neurine 
is  a  strong  base  and  gives  well-characterized  salts. 

XCH2.CH2OH 
Choline,    (CH3)3N^  ,      ethylol-trimethyl-ammo- 

nium  hydroxide,  is  a  mixed  quaternary  base  in  which  hydroxyl 
has  been  substituted  in  the  ethyl  group. 

The  constitution  of  choline  as  represented  in  the  formula  has 
been  established  by  its  synthetical  formation.  It  is  obtained  as 
one  of  the  products  of  the  hydrolysis  of  compounds  called  lecithins 
(Xejo0os,  egg-yolk)  which  are  found  in  all  animal  and  vegetable 
tissues. 

Lecithins  are  complex  compounds  which  may  be  regarded  as 
mixed  glycerol  esters  of  palmitic,  stearic,  or  ole'ic,  and  phosphoric 
acids,  combined  with  choline.  The  formula  for  stearin-lecithin, 
which  occurs  in  egg-yolk,  is 

CH2O.OC.Ci7H35 
CHO.OC.CnH35 

>^OH 
\O.CH2.CH2.^\ 

XOH 

When  boiled  with  barium  hydroxide,  barium  stearate,  (Ci7H35- 
CO.O)2Ba,  is  precipitated,  choline  is  set  free,  and  the  barium  salt 
of  glycero-phosphoric  acid,  CH2OH.CHOH.CH2.OPO(O2Ba), 
is  formed. 

The  importance  of  the  lecithins  in  the  functions  of  life  is  evi- 
dent from  their  universal  occurrence  in  the  tissues  and  especially 
in  the  nervous  tissue;  and  from  the  fact  that  they  form  a  constant 
constituent  of  milk. 

The  lecithins  are  wax-like,  hygroscopic  substances,  which  swell 


AMINES   AND   AMIDES  J  NITRO-COMPOUNDS  135 

up  in  water  to  gelatinous  masses.     They  are  soluble  in  alcohol, 
ether  and  chloroform,  and  crystallize  with  difficulty. 

Cephalin,  closely  related  to  lecithin  and  probably  as  gener- 
ally present  in  the  tissues,  is  a  derivative  of  amino  ethyl  alcohol 
as  lecithin  is  of  choline. 

Tetraalkylammonium  Hydroxides. — The  quaternary  halides 
are  obtained  by  the  direct  union  of  a  tertiary  amine  and  the  alkyl 
halide,  and  therefore  appear  in  the  mixture  of  amine  salts  formed 
by  the  reaction  of  ammonia  on  alkyl  halides.  It  has  been  already 
stated  that  the  tetraalkyl  amines  cannot  be  set  free  from  their 
salts,  like  other  amines,  by  caustic  alkalies.  When,  however, 
solutions  of  the  halide  salts  are  digested  with  silver  oxide,  silver 
halide  is  formed  and  the  solution  becomes  strongly  alkaline. 
By  evaporation  in  a  vacuum,  a  white  crystalline  mass  is  obtained 
which  is  believed  to  be  the  hydroxide  of  the  amine: 

(CH3)4NI  +  AgOH  =  (CH3)4NOH  +  Agl 

The  tetraalkyi  ammonium  hydroxides  are  very  strong  bases, 
resembling  the  caustic  alkalies  in  their  behavior.  For  this  reason 
the  caustic  alkalies  do  not  react  with  their  salts  in  aqueous  solu- 
tion; such  a  reaction  would  be  like  one  between  sodium  hydroxide 
and  potassium  chloride  with  the  formation  of  potassium  hydrox- 
ide. The  reaction  with  silver  hydroxide  is  in  consequence  of  the 
insolubility  of  silver  iodide.  Similarly,  the  hydroxides  may  be 
obtained  from  the  chlorides  by  using  potassium  hydroxide  in 
alcoholic  solution,  since  potassium  chloride  is  insoluble  in  alcohol. 

These  substituted  ammonium  hydroxides  in  solution  absorb 
carbon  dioxide  from  the  air  with  the  formation  of  carbonates, 
corrode  the  flesh,  and  saponify  fats.  When  heated,  they  decom- 
pose with  the  formation  of  tertiary  amines.  Tetramethyl 
ammonium  hydroxide,  for  example,  gives  trimethyl  amine  and 
alcohol: 

(CH3)4NOH  =  (CH3)3N  +  CH3OH 
but  the  homologous  compounds  give  an  olefine  and  water: 
(C2H6)4NOH  =  (C2H5)3N  +  C2H4  +  H2O 


136 


INTRODUCTION  TO   ORGANIC  CHEMISTRY 


AMINES 


Methyl 

PRIMARY 
Melting          Boiling 
Point              Point 

-6° 

SECONDARY 
Boiling 
Point 

7° 

TERTIARY 
Boiling 
Point 

1  S° 

Ethyl 

+  16.2 

/ 

*6 

»3O 
OO 

Propyl 
Propyl  (iso) 
Butyl 
Butyl  (iso) 
Butyl  (sec.) 

49 
32 
76 
66 
63 

*JW 

98 
84 
1  60 
136 

yvj 

156 

215 
187 

Butyl  (tert.) 

46 

Amyl  (iso) 
Hexyl 
Dodecyl 
Tridecyl 
Heptadecyl 

95 
129 

27°           248 
27             265 
49       335-340 

187 

235 

260 

Phosphines  and  Arsines 

Alkyl  derivatives  of  phosphine,  PH3,  and  of  arsine,  AsH3,  are 
known  which  are  analogous  to  the  amines.  All  of  the  classes  of 
the  amines  are  represented  in  the  phosphines.  The  primary, 
secondary,  and  tertiary  phosphines  are  weakly  basic,  but 
the  alkylphosphonium  hydroxides  (e.g.,  (CH3)4POH)  are  strong 
bases.  Primary  and  secondary  arsines  in  their  chlorine  and 
oxygen  derivatives,  such  as  CH3AsCl2,  (CH3)2AsCl,  and 
(CH3)2As.O.As(CH3)2  have  been  long  known,  and  more  recently 
the  arsines  themselves  have  been  prepared  and  investigated. 
(CH3)AsH2  boils  at  2°,  (CH3)2AsH  boils  at  36°  and  is  spontane- 
ously inflammable.  The  tertiary  arsines  such  as  (CH3)3As  have 
no  basic  properties,  but  the  quaternary  arsine  hydroxide, 
(CH3)4AsOH,  forms  salts  like  the  corresponding  phosphorus 
and  nitrogen  compounds.  We  notice  here  a  gradation  in  the 
behavior  of  amines,  phosphines,  and  arsines  which  tallies  with 
that  which  appears  in  comparing  the  other  compounds  of  nitrogen, 
phosphorus,  and  arsenic. 


AMINES   AND   AMIDES;   NITRO-COMPOUNDS  137 

Cacodyl  Oxide,  (CH3)2As.O.As(CH3)2,  is  a  liquid  of  frightful 
odor,  which  is  formed  by  distilling  arsenious  oxide  with  an  acetate: 

As2O3  +  4CH3CO.OK  = 

(CH3)2As.O.As(CH3)2  +  2K2CO3  +  2CO2 

This  substance  reacts  with  hydrochloric  acid  to  form  cacodyl 
chloride,  (CH3)2AsCl;  and  from  this,  by  the  action  of  zinc,  free 
cacodyl,  (CH3)2As.As(CH3)2,  is  produced,  as  a  spontaneously  in- 
flammable liquid. 

The  cacodyl  radical,  (CH3)2As,  enters  into  many  combinations, 
and  is  readily  transferred  by  simple  reactions  from  one  compound 
to  another.  Cacodyl  and  its  compounds  are  of  great  historical 
interest  in  the  theory  of  organic  radicals  through  their  investiga- 
tion by  Bunsen  (1837-1843).  The  compounds  of  cacodyl  have 
very  repulsive  odors  and  are  poisonous. 

The  Amides 

The  amides  may  be  denned  as  ammonias  in  which  hydrogen  is 
replaced  by  acyl  groups,  or  as  acids  whose  hydroxyl  is  replaced  by 
the  NH2  group. 

As  in  the  case  of  amines,  we  have  primary,  secondary,  and  ter- 
tiary amides,  but  quaternary  amides,  or  compounds  of  them, 
are  not  known. 

Formation. — Primary  amides  can  be  made:  i.  From  the  am- 
monium salts  of  the  acids  by  the  removal  of  the  elements  of 
water  through  heating: 

CH3.  CO.ONH4  *±  CH3.CO.NH2  +  K£) 

Acetamide 

But  since  the  ammonium  salts  of  the  fatty  acids  dissociate  to  a 
considerable  degree  into  the  acids  and  ammonia,  when  heated 
under  ordinary  pressure,  this  reaction  is  usually  carried  out  at  a 
high  temperature  (2oo°-25o°)  in  sealed  tubes.  It  is  a  reversible 
reaction  and  hence  only  a  partial  conversion  into  amide  occurs — 


138  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

under  the  above  conditions  some  75  per  cent,  of  the  theoretical 
amount  is  obtained. 

A  more  convenient  way  which  has  been  used  for  making  aceta- 
mide,  in  which  the  use  of  sealed  tubes  is  avoided,  is  by  boiling  dry 
ammonium  acetate  with  rather  more  than  its  weight  of  glacial 
acetic  acid  for  several  hours  with  a  reflux  condenser.  The  water 
is  thus  removed,  and  the  acetic  acid  on  the  principal  of  mass 
action  inhibits  the  dissociation  of  the  salt  into  acid  and  ammonia. 

2.  From  esters,  by  the  action  of  ammonia: 

CH3.CO.OC2H6  +  NH3  =  CH3.CO.NH2  +  C2H5OH 

With  esters  which  are  quite  soluble  in  water  this  reaction  goes 
easily.  The  alcohol  and  water  are  readily  removed  by  distilla- 
tion. 

3.  From  acid  chlorides  or  anhydrides: 

CH3.CO.C1  +  2NH3  =  CH3:CO.NH2    +  NH4C1 
(CH3.CO)2O  +  2NH3  =  2CH3.CO.NH2  +  H2O 

The  reaction  with  acid  chlorides  is  analogous  to  that  for  making 
amines  from  alkyl  chlorides,  but  takes  place  much  more  easily — 
in  the  case  of  acetyl  chloride,  at  room  temperature.  The  differ- 
ence is  due  to  the  presence  of  an  acid  group  (acyl)  instead  of  a 
basic  group  (alkyl).  For  the  same  reason,  the  reaction  of 
ammonia  with  acid  anhydrides  is  readily  effected,  while  the  anal- 
ogous reaction  for  the  formation  of  an  amine  from  ether  and 
ammonia  does  not  take  place  at  all. 

4.  From  nitriles  (alkyl  cyanides)  by  partial  hydrolysis.     This  is 
accomplished  by  dissolving  the  nitrile  in  concentrated  sulphuric 
acid  or  by  treatment  with  concentrated  hydrochloric  acid;  also 
by  means  of  hydrogen  peroxide  in  alkaline  solution: 

CH3CN  +  H2O  =  CH3CO.NH2 
C5HnCN  +  2H2O2  =  C5HUCO.NH2  +  O2  +  H2O 

Secondary  amides  are  formed  by  reaction  between  primary 


AMINES   AND   AMIDES;   NITRO-COMPOUNDS  139 

amides  and  acid  anhydrides,  the  acid  being  formed  at  the  same 
time: 

CH3.CO.NH2  +  (CH3.CO)2O  =  (CH3CO)2NH  +  CH3.CO.OH 

or  by  heating  nitriles  with  organic  acids: 

CH3.CN  +  CH3.CO.OH  =  (CH3.CO)2NH 

Tertiary  amides  can  be  made  by  heating  nitriles  with  acid  anhy- 
drides: 

CH3.CN  +  (CH3.CO)20  =  (CH3.CO)3N 

Neither  of  these  classes  of  amides  is  of  special  importance. 

Properties. — Formamide,  HCO.NH2  is  a  liquid.  The  other 
amides  are  crystalline  solids.  The  amides  of  the  lower  acids  are 
deliquescent  and  very  soluble  in  water.  They  distil  without  de- 
composition at  temperatures  which  are  higher  than  the  boiling 
points  of  the  corresponding  acids;  formamide,  however,  suffering 
partial  decomposition  into  ammonia  and  carbon  monoxide.  It 
may  be  noted  that  the  boiling  points  of  the  amines  are  much 
lower  than  those  of  the  hydroxyl  compounds  (alcohols)  to  which 
they  bear  the  same  relation  as  that  of  the  amides  to  the  acids. 
The  amides  usually  have  a  disagreeable  odor,  which,  however,  is 
in  most  instances  due  to  certain  impurities.  Acetamide,  for 
example,  when  carefully  purified,  is  odorless.  Amides  of  highest 
molecular  weight  are  almost  insoluble  in  water,  but  they  all 
dissolve  in  alcohol  or  ether. 

Reactions. — Certain  differences  between  amides  and  amines 
have  been  noted  in  respect  to  the  reactions  for  their  formation; 
and  similar  differences,  also  due  to  the  presence  of  an  acyl  group 
instead  of  an  alkyl  group,  are  observed  in  the  various  reactions 
into  which  they  enter.  In  the  amides  the  basic  and  acidic  proper- 
ties are  balanced  so  that  they  are  neutral  substances,  while  the 
amines  are  strong  bases. 

i.  With  strong  acids  amides  form  rather  unstable  salts,  such  as 
€H3.CO.NH2HC1. 


140  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

2.  On  the  other  hand,  the  hydrogen  atoms  of  the  NH2  group 
can  be  replaced  by  some  metals.     With  mercuric  oxide,  for  in- 
stance,  the    compound,   (CH3.CO.NH)2Hg,    is    formed,   whose 
alcoholic  solution  yields  colorless  crystals,  melting  at  195°. 

3.  The  most  characteristic  reaction  of  the  amides,  and  that  in 
which  their  difference  from  the  amines  is  most  striking,  is  their 
ready  hydrolysis,  by  which  the  bond  between  the  nitrogen  and 
carbon  is  broken,  with  the  formation  of  ammonia  and  the- cor- 
responding acid  (or  the  ammonium  salt) : 

CH3.CO.NH2  +  H2O  =  CH3.CO.OH  +  NH3 

This  hydrolysis  is  a  reversal  of  the  first  reaction  given  for  their 
formation  (p.  137),  and  occurs  when  they  are  heated  with  water 
alone,  but  more  rapidly  when  an  inorganic  acid  or  alkali  is  present 
(cf.  hydrolysis  of  esters,  p.  124).  Amines  do  not  enter  into  an 
analogous  reaction  with  water  with  the  formation  of  ammonia 
and  an  alcohol ;  but  at  high  temperatures  amides  act  on  alcohols, 
giving  either  an  ester  and  ammonia,  or  the  acid  and  a  primary 
amine: 

CH3.CO.NH2  +  CH3.OH  =  CH3.CO.OCH3  -jr  NH3 
CH3.CO.NH2  +  CH3.OH  =  CH3.CO.OH  +  CH3NH2 

4.  By  the  action  of  phosphorus   pentoxide,  the  elements  of 
water  are  withdrawn  from  amides,  with  the  production  of  nitriles, 
thus  reversing  the  reaction  by  which  they  are  formed  from  these 
compounds. 

5.  Like  the  primary  amines,  the  amides  are  changed  into  the 
corresponding   hydroxyl   compounds   (acids)   by   the  action  of 
nitrous  acid: 

CH3.CO.NH2  +  HN02  =  CH3.CO.OH  +  N2  +  H2O 

6.  The  reaction  of  amides  with  bromine  and  caustic  alkalies 
has  already  been  given  (p.  129). 


AMINES   AND   AMIDES;   NITRO-COMPOUNDS  141 

7.  Amides  are  decomposed  by  concentrated  nitric  acid  with 
evolution  of  nitrous  oxide: 

CH3.CO.NH2  +  HNO3  =  CH3.CO.OH  +  H2O  +  N2O. 

In  this  reaction  the  nitrate  of  the  amide,  CH3.CO.NH2HNO3,is 
first  formed  and  its  decomposition  is  like  that  of  ammonium 
nitrate: 

NH4N03  =  N2O  +  2H20. 

Structure  of  Amides. — We  have  assumed,  in  discussing  the 
amides,  that    the    structure    of    their    characteristic    group    is 


The  only  other  arrangement  possible  would  be 

/OH 
~ 


The  facility  with  which  an  amide  is  formed  from  an  ammonium 
salt,  and  the  easy  exchange  of  the  amido-group  for  the  hydroxyl 
are  in  favor  of  the  first  formula.  The  second  formula  with  its 
hydroxyl  group  calls  for  an  alcoholic  character  which  is  not  indi- 
cated by  most  of  the  behavior  of  the  amide.  In  the  compound 
which  acetamide  forms  with  mercury,  however,  there  is  reason  for 
believing  that  the  metal  is  linked  to  carbon  by  oxygen,  so  that  this 
substance  is  probably  derived  from  a  compound  with  the  second 
formula.  Unfortunately  this  question  cannot  be  settled,  as  in 
other  cases,  by  studying  chlorine  replacement  products  formed  by 
the  action  of  phosphorus  pentachloride,  because  these  products, 
if  formed  at  all,  are  very  unstable,  breaking  down  almost  at  once 
into  nitriles.  Since  the  first  formula  agrees  with  most  of  the  facts, 
it  is  taken  as  representing  the  ordinary  structure  of  amides. 


INTRODUCTION   TO   ORGANIC   CHEMISTRY 

AMIDES 

Melting  Boiling 

Point  Point 

Formamide  HCO.NH2  -i°           200-212° 

Acetamide  CH3.CO.NH2  83                222 

Propionamide  C2H5.CO.NH2  79                213 

Butyramide  C3H7.CO.NH2  115                216 

Butyramide  (iso)  C3H7.CO.NH2  128-129        216-220 

Valeramide  C4H9.CO.NH2  u4-n6(?) 

Capronamide  C6HU.CO.NH2  100                255 

Heptylamide  C6Hi3.CO.NH2  95            250-258 

Caprylamide  C7Hi6CO.NH2  105-106 

Pelargonamide  C8Hi7.CO.NH2  99 

Capramide  C9H19.CO.NH2  98 

Palmitamide  Ci6H3i.CO.NH2  106-107 

Stearamide  CnH36.CO.NH2  109 

Nitre-paraffins 

Hydrocarbons  in  which  one  or  more  hydrogen  atoms  have  been 
replaced  by  the  —  NO2  group,  with  a  direct  linkage  of  nitrogen 
to  carbon,  are  called  nUro-compounds.  In  the  benzene  series  of 
hydrocarbons,  these  compounds  are  of  great  importance,  and  are 
readily  made  by  the  action  of  nitric  acid  upon  the  hydrocarbons; 
but  the  nitre-paraffins  are  seldom  formed,  and  then  in  small 
amount,  when  nitric  acid  is  forced  to  act  on  the  indifferent  hydro- 
carbons. They  are  relatively  unimportant  and  were  not  known 
until  1872.  They  are  briefly  described  here  because  of  their 
relation  to  the  amines. 

Formation. — The  most  important  method  for  making  the  nitro- 
paraffins  is  by  adding  an  alkyl  iodide  gradually  to  solid  silver 
nitrite: 

CH3.CH2I  +  AgNO2  =  CH3.CH2.NO2  +  Agl 

Except  in  the  case  of  the  methyl  compound,  the  distillate  from 
this  reaction  contains  two  substances  which  are  readily  separated 
by  redistillation,  as  their  boiling  points  are  widely  different.  Both 


AMINES   AND   AMIDES;   NITRO-COMPOUNDS  143 

of  the  ethyl  derivatives  have  the  percentage  composition  and  the 
molecular  weight  indicated  by  the  formula  given  above.  The 
one  with  the  lower  boiling  point  is  readily  hydrolyzed  with  the  for- 
mation of  alcohol  and  nitrous  acid;  and  by  nascent  hydrogen  it 
is  reduced  to  alcohol  and  ammonia  or  hydroxylamine  (cf.  p.  122). 
It  is  evidently  ethyl  nitrite  or  nitrous  ester,  with  the  formula 
CH3.CH2O.N:O.  The  isomeric,  higher  boiling  compound,  is  not 
hydrolyzed,  and  on  reduction  gives  an  amine,  CH3.CH2-NH2. 
We  conclude  from  these  facts  that  this  is  a  true  nitro-compound 
with  the  nitrogen  directly  united  to  carbon;  while  in  the  ester  it  is 
linked  to  carbon  by  oxygen.  The  structure  of  the  nitro-compound 


is,  therefore,  CH3.CH2. 


// 
N^t 


Nitro-compounds  are  not  produced  from  alkyl  halides  by  the 
action  of  other  nitrites,  such  as  NaNO2  or  KNO2.  Silver  nitrite 
appears  therefore  to  have  a  different  constitution  from  other 
nitrites  and  to  be  Ag.NO2  with  some  Ag.O.NO. 

Properties.  —  The  nitro-paraffms  are  liquids  of  pleasant  odor, 
which  distil  without  decomposition,  and  are  almost  insoluble  in 
water.  The  lower  ones  are  heavier  than  water,  but  the  specific 
gravity  grows  less  as  the  number  of  carbon  atoms  increases,  that 
of  nitrobutane  being  already  lighter  than  water.  The  lower 
nitro-paraffins  have  acid  characteristics,  due  to  the  strongly  nega- 
tive nature  of  the  NO2  group.  They  dissolve  in  aqueous  solutions 
of  alkalies,  and  are  precipitated  from  these  solutions  by  acids. 
From  an  alcoholic  solution  of  sodium  hydroxide  a  sodium  salt, 
CH3.CHNa.NO2  is  precipitated.  These  salts  decompose  explo- 
sively when  heated.  The  most  important  reaction  of  the  nitropar- 
afnns  is  that  of  their  reduction  to  amines  by  "nascent"  hydrogen. 

The  introduction  of  more  than  one  nitro  group  cannot  usually  be 
effected  directly,  and  only  a  few  of  the  more  highly  nitrated  paraf- 
fins have  been  made.  Dinitromethane,  CH2(NO2)2,  and  trinitro- 
methane,  CH(NO2)3,  "  nitroform,"  are  unstable  oils,  the  latter  ex- 
ploding violently  when  heated.  Tetranitromethane,  C  (NO  2)  4,  how- 
ever, is  a  stable  liquid  that  can  be  distilled  without  decomposition. 


CHAPTER  XI 
CYANOGEN  AND  CYANOGEN  COMPOUNDS 

The  student  has  already  learned,  in  inorganic  chemistry,  some- 
thing about  cyanogen,  and  has  become  acquainted  with  certain 
cyanogen  compounds,  particularly  with  potassium  cyanide,  and 
potassium  ferro  and  ferricyanides,  which  are  used  as  reagents 
in  analysis.  In  the  first  chapter  of  this  book  the  formation  of 
sodium  cyanide,  on  heating  a  nitrogen-containing  organic  sub- 
stance with  sodium,  was  given  as  a  means  for  the  detection  of 
nitrogen.  Nearly  all  nitrogenous  organic  substances  react  in  this 
way  with  sodium  or  potassium,  and  on  digestion  of  the  soluble 
cyanide  with  a  ferrous  salt,  the  f errocyanide  of  sodium  or  potassium 
is  formed. 

The  chief  sources  of  the  cyanogen  compounds  are : 

1.  Potassium  f  errocyanide,  which  is  made  commercially  by 
heating  a  mixture  of  crude  potash  (K2CO3),  scrap  iron,  and  refuse 
animal  substances,  such  as  clippings  of  leather  or  horn,  or  dried 
blood,  and  treating  the  mass,  after  cooling,  with  water.     Yellow 
crystals  of  the  ferrocyanide  are  obtained  from  this  solution.     From 
the  ferrocyanide,  potassium  cyanide,  KCN,  is  obtained  by  heating 
it  alone  or  with  potassium  carbonate. 

2.  Sodium  cyanide,  NaCN,  is  made  in  large  quantities  by  pass- 
ing ammonia  over  sodium  at  3oo°-4oo°,  and  decomposing  the 
sodium  amide,  NaNH2,  thus  formed,  by  carbon  at  a  red  heat: 

2Na  +  2NH3  =  2NaNH2  +  H2 

NaNH2  +  C  =  NaCN  -f-  H2 

Sodium  cyanide  may  also  be  successfully  manufactured  by  a 

144 


CYANOGEN  AND  CYANOGEN  COMPOUNDS       145 

method  recently  described  by  J.  E.  Bucher1  in  which  nitrogen 
reacts  with  a  mixture  of  sodium  carbonate  and  powdered  coke 
at  a  red  heat  in  the  presence  of  finely  divided  iron  as  a  catalyst: 

Na2C03  +  4C  +  N2  (+  Fe)  -  2NaCN  +  3CO  (+  Fe) 
Producer  gas  may  be  used  to  furnish  the  nitrogen,  and  in  this 
case  the  carbon  monoxide  of  the  gas,  under  the  catalyzing  effect 
of  the  iron,  yields  a  continuous  supply  of  finely  divided  carbon: 

CO  +  C  <=±  CO2  +  38,080  calories 

Compounds  containing  cyanogen  are  also  obtained  by  heating 
the  carbides  of  calcium  or  barium  in  nitrogen.  The  calcium  com- 
pound, CN.NCa,  calcium  cyanamide,  "  nitrolime,"  is  manu- 
factured on  a  large  scale  from  calcium  carbide  and  nitrogen 
from  liquid  air.  It  slowly  decomposes  in  the  soil,  producing 
ammonia:  CN.NCa  +  3H2O  =  2NH3  +  CaCO3 

and  is  used,  on  this  account,  as  a  fertilizer,  thus  making  atmos- 
pheric nitrogen  available  for  plant  life.  With  superheated  steam 
all  the  nitrogen  of  cyanamide  is  converted  into  ammonia  which  is 
now  prepared  commercially  in  this  way.  Cyanamide  on  fusion 
with  salts  of  alkalies  and  carbon  yields  the  alkali  cyanide: 

CN.NCa  +  C  H-  2NaCl  =  NaCN  +  CaCl2 

Cyanogen  (CN)2. — The  cyanogen  radical,  CN,  can  be  trans- 
ferred from  one  compound  to  another  like  the  halogen  atoms; 
and  like  them  it  is  incapable  of  independent  existence,  but  when 
forced  from  combination  unites  with  itself  forming  molecules  of 
(CN)2,  similar  to  the  diatomic  molecules  of  chlorine,  etc.  The 
evidence  for  this  is  its  molecular  weight  as  found  from  its  density. 

Cyanogen  is  formed  when  ammonium  oxalate  is  strongly 
heated  with  phosphorus  pentoxide : 

CO.ONH4  CN 

|  -  4H20  =   |       or  (CN)2 

CO.ONH4  CN 

1  Journal  of  Industrial  and  Engineering  Chemistry,  IX,  233  (1917). 


146  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

This  reaction,  and  the  fact  that  an  intermediate  product,  oxamide, 
CO.NH2 

|  ,  can  be  made  both  from  ammonium  oxalate  and  from 

CO.NH2 

cyanogen,  are  evidence  that  cyanogen  is  the  nitrile  of  oxalic 
acid,  and  from  the  known  structure  of  oxalic  acid  (p.  178)  we 

C=N  N=C 

conclude  that  that  of  cyanogen  is   |  and  not    |  ,  which 

C=N  N=C 

would  be  the  other  possible  arrangement  with  tetrad  carbon. 
Preparation. — Cyanogen    is    prepared    by    heating    mercuric 
cyanide: 

Hg(CN)2  =  (CN)2  +  Hg 

or  more  conveniently  by  slowly  adding  a  solution  of  copper  sul- 
phate to  a  warm  solution  of  potassium  cyanide.  The  cupric 
cyanide  first  formed  decomposes  readily  into  cuprous  cyanide, 
CuCN,  and  cyanogen.  Cyanogen  is  also  a  product  of  the  electro- 
lysis of  sodium  cyanide. 

Properties. — Cyanogen  is  a  poisonous  gas  of  characteristic 
pungent  odor.  It  burns  with  a  purple-fringed  flame.  It  is 
somewhat  soluble  in  water,  but  the  solution  is  unstable.  A  brown 
solid  separates,  and  the  solution  contains  oxalate  and  carbonate 
of  ammonia,  hydrocyanic  acid,  and  urea.  A  polymeric  form  of 
cyanogen  of  unknown  molecular  weight  is  produced  in  the  form  of 
a  brown  solid  as  a  by-product  in  making  cyanogen  from  mercuric 
cyanide;  and  in  the  electrolysis  of  potassiun  cyanide  all  of  the 
cyanogen  is  converted  into  this  modification,  which  is  called 
paracyanogen.  At  860°  this  changes  to  cyanogen. 

Cyanogen  is  readily  converted  into  oxamide  (p.  180)  when  led 

nto  hydrochloric  acid  containing  44  per  cent,  of  hydrogen  chlo- 
ride. On  heating  the  oxamide  with  the  concentrated  acid,  the 
hydrolysis  to  oxalic  acid  is  quickly  completed  (Bucher).  When 
led  into  solutions  of  potassium  hydroxide,  cyanogen  forms  com- 
pounds analogous  to  those  given  by  chlorine  or  bromine,  namely, 
potassium  cyanide,  KCN,  and  cyanate,  KOCN. 


CYANOGEN  AND  CYANOGEN  COMPOUNDS       147 

Hydrocyanic  acid,  HCN,  commonly  known  as  prussic  acid, 
occurs  in  all  parts  of  a  tree,  Pangium  edule,  which  is  native  in 
Java.  The  seed-kernels  of  this  tree  are  a  deadly  poison,  but  by 
soaking  in  flowing  water  the  hydrocyanic  acid  is  removed,  and 
they  are  then  used  by  the  Malays  as  food.  A  substance  called 
amygdalin  which  occurs  in  the  leaves  of  laurel  and  cherry,  and  in 
the  kernels  of  peach-stones,  in  bitter  almonds,  and  other  sub- 
stances, when  softened  by  water,  usually  undergoes  a  fermentation, 
one  of  whose  products  is  prussic  acid. 

Hydrocyanic  acid  is  readily  made  by  distilling  potassium  cyan- 
ide or  potassium  ferrocyanide  with  dilute  sulphuric  acid: 

2K4Fe(CN)6  +  3H2S04  =  6HCN  +  3K2SO4  + 

FeK2Fe(CN)6 
Ferrous  potassium  ferro-cyanide 

(Concentrated  sulphuric  acid  with  the  ferroeyanide  yields  no 
hydrocyanic  acid,  but  carbon  monoxide.)  The  distillate  is  a 
dilute  solution  of  hydrocyanic  acid.  The  anhydrous  acid  is 
obtained  by  drying  the  vapors  from  this  reaction  by  means  of 
calcium  chloride  and  condensing  them  by  a  freezing  mixture. 

Properties. — The  anhydrous  acid  is  a  volatile  liquid,  boiling  at 
26°.  It  has  the  odor  of  bitter  almonds,  and  burns  with  a  violet 
flame.  When  unmixed  with  water  the  acid  can  be  kept  without 
change,  but  its  solutions  are  unstable,  depositing  a  brown  sub- 
stance with  the  production  of  ammonium  formate  and  other 
compounds.  This  decomposition  is  retarded  by  the  presence  of 
a  very  small  amount  of  an  inorganic  acid.  Hydrocyanic  acid  is  a 
very  weak  acid,  hardly  reddening  litmus  paper.  It  does  not 
decompose  carbonates,  but,  on  the  contrary,  is  set  free  from  its 
salts  by  carbonic  acid;  and,  in  consequence,  potassium  cyanide 
always  smells  of  prussic  acid  when  exposed  to  the  air.  Hydro- 
cyanic acid  and  the  cyanides  which  contain  the  ion  CN  are  very 
powerful  and  rapidly  acting  poisons.  Complex  ions  containing 
cyanogen,  like  Fe(CN)6,  in  solutions  of  potassium  ferro-  and 
ferricyanides,  are  not  poisonous. 


148  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

Structure. — Two  structural  formulas  for  hydrocyanic  acid  can 
be  written:  H-C=N,  and  H-N  =  C,  or  H-N=C.1 

'From  the  structure  agreed  on  for  cyanogen,  N  =  C  —  C = N,  the 
first  of  these,  H  — C  =  N,  is  indicated.  Some  reactions  are  better 
explained  by  this  formula,  some  by  the  second,  and  some  are 
equally  well  explained  by  either.  The  first  formula  is  that  of  a 
nitrile  of  formic  acid,  and  hydrocyanic  acid  can  be  hydrolyzed  to 
formamide  and  to  formate  of  ammonium,  and  the  reverse  reac- 
tions can  also  be  carried  out: 


HC  ^N  -f  H20  <±  HC<  +  H20  +±  HC 


By  nascent  hydrogen  hydrocyanic  acid  is  converted  into  methyl 
amine: 

H-C=N  +  4H  =  CH3.NH2 

As  nitrogen  readily  changes  its  valence  from  three  to  five  and 
from  five  to  three,  these  reactions  might  be  written  with  the  second 
formula. 

When  potassium  cyanide  acts  on  an  alkyl  halide,  a  nitrile  is 
formed  in  which  the  carbon  of  the  cyanogen  group  is  certainly 
united  to  the  CH3  group: 

CH3I  +  KCN  =  CH3CN  +  KI 

But  this  again  could  be  explained,  through  change  of  valence,  by 
the  other  formula.  Silver  cyanide,  however,  with  an  alkyl  halide, 
gives  an  isomeric  compound  whose  .  structure  has  been  proved 
to  be  CH3.N  =  C,  or  CH3.N  =  C.  The  cyanogen  group  appears, 
therefore,  in  both  arrangements,  —  C  =  N  and  —  N  =  C  or 
—  N  =  C.  The  former  is  that  usually  adopted  as  that  of 
hydrocyanic  acid,  whose  formula  is  therefore  written,  H—  C=N; 
while  the  isomeric  form,  H—  N  =  CorH—  N=C,  is  called 
isohydrocyanic  acid;  the  group  —  N  =  C  or  —  N  =  C  being 

1  In  this  formula,  and  others  which  will  be  discussed,  carbon  is  represented 
as  divalent  or  unsaturated,  as  it  is  in  CO. 


CYANOGEN  AND  CYANOGEN  COMPOUNDS       149 

called  the  isocyanogen  group.  Both  of  the  possible  forms  may  be 
present  together.  The  great  difficulty  in  deciding  this  question 
is  the  absence  of  an  alkyl  group.  When  such  a  group,  instead  of 
hydrogen,  is  combined  with  cyanogen,  the  decision  is  easily  made 
by  finding  whether,  in  reactions  by  which  the  molecule  is  broken 
up,  the  carbon  or  the  nitrogen  atom  of  the  CN  group  remains 
attached  to  the  alkyl. 

For  the  properties  anfl  uses  of  the  salts  of  hydrocyanic  acid,  and 
of  the  ferro  and  ferricyanides  of  the  metals  the  student  is  referred 
to  his  text-book  on  inorganic  chemistry. 

Cyanogen  chloride,  CN.C1,  is  a  very  poisonous  compound  which 
is  formed  when  chlorine  is  brought  into  a  solution  of  hydrocyanic 
acid.  It  boils  at  15.5°,  and  is  somewhat  soluble  in  water.  On 
keeping,  it  partly  polymerizes  to  cyanuric  chloride,  C3N3Cl3. 
With  ammonia  it  gives  cyanamide,  CN.NH2.  With  potassium 
hydroxide,  potassium  cyanate,  CN.OK,  is  formed: 

CN.C1  +  2KOH  =  CN.OK  +  KC1  +  H2O 

Cyanamide,  CN.NH2,  is  a  colorless,  crystalline  solid,  melting 
at  40°.  It  is  readily  soluble  in  water,  alcohol,  and  ether.  The 
hydrogen  of  its  amido-group  is  replaceable  by  metals.  Silver 
cyanamide,  CN.NAg2,  which,  unlike  most  silver  salts,  is  almost 
insoluble  in  ammonia,  is  precipitated  from  an  ammoniacal  solution 
of  silver  nitrate  by  cyanamide.  The  industrial  manufacture  of 
calcium  cyanamide,  CN.NCa,has  already  been  referred  to  (p.  145). 

Cyanuric  acid,  (CNOH)3,  is  formed  when  cyanuric  chloride  is 
boiled  with  water,  and  is  also  one  of  the  products  obtained  when 
urea,  CO(NH)2,  is  heated: 

3CO(NH2)2  =  (CNOH)3  +  3NH3 

It  crystallizes  from  water,  in  which  it  is  sparingly  soluble,  with  two 
molecules  of  water  of  crystallization,  and  forms  well  characterized 
salts. 
Cyanic  acid,  (H— O  —  C=N,  is  made  by  heating  anhydrous 


150  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

cyanuric  acid  in  a  current  of  carbon  dioxide,  and  condensing  the 
gas  which  is  formed  in  a  receiver  surrounded  by  a  freezing 
mixture.  It  is  a  very  volatile  liquid,  and  unstable,  polymerizing 
rapidly  at  o°  to  cymelide,  (HOCN)X,  a  solid  of  unknown  molecular 
weight,  which  regenerates  cyanic  acid  on  heating.  In  aqueous 
solution,  cyanic  acid  decomposes  at  temperatures  above  o°  into 
carbon  dioxide  and  ammonia: 

HOCN  +  H2O  =  C02  +  NH3 

Potassium  cyanate,  K  —  O  —  C  =N,  is  formed  by  the  reaction  of 
cyanogen  chloride  and  potassium  hydroxide  (p.  149);  but  is 
usually  prepared  by  the  oxidation  of  potassium  cyanide  through 
heating  it  with  lead  oxide,  or  by  heating  a  mixture  of  potassium 
ferrocyanide  and  dichromate.  The  readiness  with  which  potas- 
sium cyanide  is  oxidized  to  the  cyanate  explains  its  use  as  a  reduc- 
ing agent  in  inorganic  chemistry.  The  cyanate  is  extracted  from 
the  resulting  mass  by  boiling  with  80  per  cent,  alcohol,  and  is 
obtained  on  evaporation  of  the  solvent  as  a  white  crystalline  pow- 
der. It  is  very  soluble  in  water,  and  is  slowly  hydrolyzed  in 
solution  into  ammonium  and  potassium  carbonates. 

When  hydrochloric  acid  is  added  to  its  solution,  the  cyanic  acid 
set  free  decomposes  at  once  into  carbon  dioxide  and  ammonia. 
From  the  potassium  cyanate  other  cyanates  can  be  formed  by  dou- 
ble decomposition.  The  ammonium  salt  NH4OCN  is  of  especial 
interest  because  of  its  ready  transformation  into  urea  (p.  231). 

Ammonium  Cyanate  may  be  prepared  from  sodium  cyanide  by 
leading  carbon  dioxide  and  ammonia  in  to  its  solution;  the  reaction 
being  exactly  similar  to  that  of  the  ammonia-soda  process,  the 
radical  —  CNO  taking  the  place  of  chlorine  in  the  sodium  chloride 
(Bucher): 

NaOCN  +  NH3  +  CO2  +  H2O  =  NaHCO3  +  NH4OCN 
Esters  of  cyanic  acid  have  not  been  isolated,  the  reactions 
which  should  give  them  yielding  the  polymeric  cyanuric  esters. 


CYANOGEN  AND  CYANOGEN  COMPOUNDS 

These  exist  in  two  isomeric  forms,  in  one  of  which  the  alkyl 
group  is  linked  to  the  CN  group  by  oxygen,  and  in  the  other  is 
directly  united  to  the  nitrogen  of  the  group.  These  relations  are 
proved  by  the  products  of  hydrolysis:  one  form  of  ester  giving 
cyanuric  acid  and  an  alcohol,  and  the  other  producing  primary 
amines  and  carbon  dioxide: 

(CH3.OCN)3  +  3H2O  =  3CH3OH  +  (HOCN)3 
(CH3.NCO)3  +  3H20  =  3CH3NH2 


There  thus  appear  to  be  at  least  two  isomeric  cyanuric  acids  — 
one  containing  a  hydroxyl  group,  called  cyanuric  acid;  and  an- 
other in  which  there  is  no  hydroxyl  group  and  where  the  hydrogen 
is  united  directly  with  nitrogen  —  the  isocyanuric  acid.  Two 
cyanic  acids:  normal,  HOC  =  N  and  iso,  HN  =  C  =  O,  correspond 
to  these.  Both  forms  may  be  present  together  in  some  of  the 
compounds. 

Fulminic  Acid  and  Fulminates.  —  When  ethyl  alcohol  is  added  to 
a  mixture  of  mercuric  nitrate  and  nitric  acid  a  rather  violent  reac- 
tion occurs,  with  danger  of  explosion  unless  precautions  are  taken. 
After  the  reaction  is  finished,  and  as  the  solution  cools,  white 
crystals  are  precipitated  which  have  the  composition  Hg(CNO)2. 
A  corresponding  silver  salt  is  formed  under  similar  conditions. 
These  salts,  when  dry,  explode  with  great  violence  when  heated 
or  struck;  and  the  mercury  compound  is  the  substance  used  in 
percussion  and  fulminating  caps  for  firing  gunpowder,  dynamite 
and  smokeless  powders.  The  composition  of  these  fulminates 
shows  them  to  be  salts  of  fulminic  acid,  which  is  a  third  isomer  of 
cyanic  acid.  When  sodium  fulminate  (formed  by  the  action  of 
sodium  amalgam  on  the  mercury  salt)  is  treated  with  hydrochloric 
acid  at  o°,  an  unstable  crystalline  compound  is  produced  whose 

/H 
structure  has  been  shown  to  be  HO  .  N  =  C\       •    This  substance 


is  regarded  as  an  addition  product  of  fulminic  and  hydrochloric 
acids,  and  the  formula  of  fulminic  acid  is  inferred  to  be 
H  —  O  —  N  =  C,  in  which  the  carbon  atom  acts  as  a  dyad. 


152  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

Fulminic  acid  is  too  unstable  to  be  isolated,  though  it  probably 
can  exist  in  vapor  and  in  solution.  When  fulminates  are  treated 
with  hydrochloric  acid,  a  prussic  acid  odor  is  perceived,  which  is 
evidently  due  to  traces  of  fulminic  acid.  The  fulminates  are 
nearly  if  not  quite  as  poisonous  as  hydrocyanides. 

A  special  historical  interest  attaches  to  the  fulminates,  because 
of  Liebig's  demonstration  in  1823  that  the  two  different  com- 
pounds, silver  cyanate  and  silver  fulminate  had  the  same  composi- 
tion. This  was  the  first  case  discovered  of  two  different  sub- 
stances with  the  same  composition;  and  it  was  to  designate  this 
phenomenon  that  Berzelius  proposed  the  name  isomerism. 

It  is  seen  that  it  is  not  a  simple  matter  to  determine  the  struc- 
ture of  the  cyanogen  compounds,  and  the  task  is  complicated  by 
an  apparent  mobility  in  the  arrangement  of  the  atoms,  so  that  in 
some  cases,  at  least,  we  must  assume  two  forms  to  be  present  in 
the  same  compound,  or  to  shift  easily  in  the  course  of  the  reactions. 

The  possible  arrangements  of  HCNO  are  four: 
i.  H— O— C  =  N;  2.  H— O— N  =  C(orH— O— N  =  C);  3.  H— C 
=  N  =  O;  4.  H — N  =  C  =  O.     The  generally  accepted  view  is  that 
the  first  represents  cyanic  acid,  the  fourth,  isocyanic  acid,  and  the 
second  fulminic  acid. 

Thiocyanic  Acid  and  Thiocyanates. — Sulphur  combines  directly 
with  cyanides  of  the  metals  forming  thiocyanates.  For  instance, 
when  a  solution  of  potassium  cyanide  is  boiled  with  sulphur,  the 
salt,  K— S— C  =  N,  is  produced.  The  acid,  H— S — C  =  N,  is 
obtained  in  dilute  solution  by  distilling  this  or  the  barium  salt  with 
sulphuric  acid.  The  anhydrous  acid  is  a  very  volatile  liquid  of 
sharp  odor,  which,  like  the  cyanic  acid,  polymerizes  very  readily. 
In  dilute  solutions  the  acid  is  stable,  but  in  strong  solutions  it 
decomposes  into  hydrocyanic  acid  and  persulphocyanic  acid, 
H2C2N2S 3.  The  strength  of  thiocyanic  acid  approaches  that  of  the 
halogen  acids.  Thiocyanates  are  converted  into  cyanides  by 
melting  them  with  zinc. 

The  salts  of  thiocyanic  acid  are  obtained  as  a  by-product  in  the 


CYANOGEN  AND  CYANOGEN  COMPOUNDS       153 

coal  gas  industry,  and  are  used  as  mordants.  With  the  exception 
of  the  copper,  mercury,  and  silver  salts,  the  thiocyanates  are  sol- 
uble in  water.  Potassium  and  ammonium  thiocyanates  solutions 
are  well-known  reagents  for  ferric  salts,  giving  a  blood-red  color 
even  in  very  dilute  solutions.  Mercury  thiocyanate,  when  hea'ted, 
decomposes  with  the  production  of  an  extraordinarily  voluminous 
ash,  and  is  used  in  making  the  "Pharaoh's  serpents."  The 
ammonium  salt,  when  melted,  is  partly  transformed  into  thio-urea, 
CS(NH2)2. 

Esters  of  thiocyanic  acid  are  obtained  by  the  action  of  alkyl 
iodides  on  the  thiocyanates: 

K-S-C  =  N  +  CH3I=  CH3-S-C  =  N  +  KI 

These  alkyl  thiocyanates  are  converted  into  isothiocyanates, 
such  as  CH3  — N  =  C  =  S,  by  heating.  Thus,  distillation  of 
allyl  thiocyanate,  CH2:CH.CH2—  S  — C  =  N,  causes  the  change 
into  CH2:CH.CH2-N  =  C  =  S.  This  compound,  allyl  iso- 
thiocyanate,  was  first  obtained  as  an  oil  from  mustard  seeds  where 
it  is  present  as  a  glucoside,  and  the  name  of  mustard  oils  is  given 
to  the  group  of  isothiocyanic  acid  esters  on  this  account. 

ALKYL  CYANIDES  AND  ISOCYANIDES 

In  the  discussion  of  the  structure  of  hydrocyanic  acid  it  was 
stated  that  the  action  of  silver  cyanide  on  an  alkyl  halide  gave  a 
different  compound  from  that  obtained  when  potassium  cyanide 
was  used.  The  two  compounds  are  isomeric,  that  produced  by 
potassium  cyanide  probably  having  the  structure  of  the  cyanide 
or  nitrile,  CH3C  =  N,  while  the  other  is  an  isocyanide  with  the 
formula,  CH3.N  =  C  or  CH3.N  =  C. 

Alkyl  Cyanides  or  Nitriles. — These  compounds  are  esters  of 
hydrocyanic  acid,  as  the  first  name  indicates,  but  their  ready 
hydrolysis  into  ammonium  salts  or  acids  is  their  most  interesting 
characteristic,  and  hence  they  are  more  often  designated  as  nitriles. 
Thus,  CH3.CN  is  methyl  cyanide  or  acetonitrile.  They  are 
formed  i.  by  the  withdrawal  of  the  elements  of  water  from  the 


154  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

ammonium  salts  of  acids,  the  acid  amide  being  an  intermediate 
product  (p.  100);  2.  By  the  action  of  potassium  cyanide  on 
alkyl  halides  (p.  35);  or  by  distilling  the  potassium  salt  of  an 
alkyl  sulphuric  acid  with  potassium  cyanide: 

C2H6.KSO4  +  KCN  =  C2H5.CN  +  K2SO4 

In  these  reactions  small  amounts  of  the  isocyanide  (or  isonitrile} 
are  formed.  There  are  also  other  less  important  methods  by 
which  nitriles  can  be  formed. 

The  nitriles  show  the  gradation  in  physical  properties  which  is 
familiar  in  all  homologous  series  of  compounds.  The  lower 
members  are  liquids  of  not  unpleasant  odor,  and  are  soluble  in 
water. 

The  hydrolysis  of  the  nitriles  into  acid  amides  and  ammonium 
salts,  and  their  conversion  into  primary  amines  by  nascent  hydro- 
gen, have  already  been  sufficiently  discussed. 

Alkyl  isocyanides  or  isonitriles  are  formed,  as  has  been  stated, 
by  treatment  of  an  alkly  halide  with  silver  cyanide.  Some  nitrile 
is  produced  at  the  same  time.  Another  reaction  for  making  the 
isocyanides  is  carried  out  by  heating  a  primary  amine  with  an 
alcoholic  solution  of  chloroform  and  potassium  hydroxide: 


C2H5.NH2  +  CHC13  +  3KOH  =  C2H6.NC  +  3KC1 

Since  in  this  reaction,  a  carbon  atom  replaces  the  two  hydrogen 
atoms  of  the  amino-group,  the  compounds  are  often  given  a  third 
name,  carbylamines,  which  indicates  this  relation.  This  reaction 
is  employed  as  a  test  for  primary  amines  (p.  132). 

The  isonitriles  are  volatile  liquids  of  an  almost  unbearable  odor, 
lighter  than  water  and  soluble  in  it.  They  are  readily  decomposed 
by  water  in  the  presence  of  inorganic  acids  into  amines  and  formic 
acid: 

C2H5.NC  +  2H2O  =  C2H5.NH2  -f  H.CO.OH 

Both  the  formation  of  these  compounds  and  the  mode  of  their 


CYANOGEN  AND  CYANOGEN  COMPOUNDS      1540 

hydrolysis  justify  the  name  of  carbylamine,  and  are  evidence  for 
the  structure  which  is  assigned  to  them: 

C2H5.N  =  C  or  C2H5.N  =  C 

Alkyl  Isocyanates  such  as  C2H5NCO,  are  volatile  liquids  of 
penetrating  and  very  disagreeable  odor.  They  are  formed  by 
the  action  of  silver  cyanate  on  alkyl  halides,  and  by  oxidation 
of  isonitriles  with  mercuric  oxide.  When  heated  with  alkalies, 
they  give  primary  amines  and  alkali  carbonate  (p.  129).  With 
ammonia  or  amines  they  produce  alkyl-substituted  ureas: 

/NH.C2H5 


Hence,  when  boiled  with  water,  they  yield  symmetrical  dialkyl 
ureas,  the  amine  formed  at  first  reacting  with  excess  of  ester: 

C2H5.NCO  +  H2O  =  CO2  +  C2H5.NH2 
and  C2H5.NCO  +  C2H5.NH2  =  CO(NH.C2H5)2 


CHAPTER  XII 

ALCOHOLS  WITH  MORE  THAN  ONE  HYDROXYL 
GROUP 

Besides  the  alcohols  with  one  hydroxyl  group,  which  have  been 
studied,  there  are  many  compounds  known  which  are  shown  by 
their  reactions  to  contain  two  or  more  hydroxyl  groups.  These 
polyhydroxyl  compounds  show  the  characteristic  alcohol  reactions 
and  hence  belong  to  the  general  group  of  alcohols. 

The  simplest  formula  which  can  be  written  for  a  dihydroxyl 
derivative  of  a  paraffin  is  CH2(OH)2.  Such  a  compound,  however, 
cannot  be  made,  nor  can  other  similar  compounds,  such  as 
CH3.CH(OH)2,  be  obtained.  Methods  which  should  give  these 
compounds  in  which  two  hydroxyl  groups  are  united  to  a  single 
carbon  atom,  such  as: 

CH3.CHI2 '+  2AgOH  =  CH3.CH(OH)2  +  2AgI 

always  result,  as  we  have  seen  (p.  H3a),  in  the  formation  of  the 
aldehyde  group  —  C  =  O.H,  instead  of  the  group  —  CH.(OH)2. 
The  Glycols. — The  simplest  polyhydroxyl  derivative  is,  there- 
fore, CH2OH.CH2OH.  This  is  called  glycol,  ethylene  glycol,  or 
ethylene  alcohol.  It  is  the  first  member  of  a  series  of  "glycols" 
which  have  the  general  formula  CnH2n(OH)2.  The  isomeric 
higher  glycols  are  distinguished  as  a,  /3,  7,  5,  etc.,  glycols  accord- 
ing as  the  hydroxyl  groups  are  united  to  adjacent  carbon  atoms 
or  to  those  farther  apart.  Thus,  of  the  butylene  glycols,  CH3.- 
CH2.CHOH.CH2OH  is  the  a-compound,  CH3.CHOH.CH2.- 
CH2OH,  the  ft  and  CH2OH.CH2.CH2.CH2OH,  the  7  glycol. 
(This  notation  is  also  employed  to  designate  the  positions  of  other 
substituting  radicals  or  atoms  in  hydrocarbon  derivatives.) 

155 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  156 

Since  in  the  higher  glycols  derived  from  the  normal  hydro- 
carbons the  alcohol  groups  may  both  be  primary,  both  secondary, 
or  one  primary  and  one  secondary,  and  in  isomeric  derivatives  we 
may  have  both  primary,  both  secondary,  or  both  tertiary,  or  any 
combination  of  the  three,  the  number  of  glycols  which  are  theo- 
retically possible  is  exceedingly  great — far  greater  than  the  number 
of  possible  hydrocarbons.  Very  few  of  them,  however,  have  been 
made. 

Preparation. — i.  The  glycols  may  be  made  by  replacing  the 
halogen  in  paraffin  dihalides  with  hydroxyl,  as  in  the  making  of 
monohydroxyl  alcohols;  but  the  action  of  potassium  hydroxide 
is  usually  so  vigorous  that  unsaturated  monohalide  compounds 
or  acetylene  hydrocarbons  are  formed: 

(CH2C1.CH2C1  +  2KOH  =  CH2OH.CH2OH  +  2KC1) 
CH2C1.CH2C1  +  KOH  =  CHC1:CH2  +  KC1  +  H2O,  and 
CHC1  :  CH2  +  KOH  =  CHi  CH  +  KC1  +  H2O 

The  reaction  succeeds,  however,  when  sodium  carbonate  is  used^ 
or  when  organic  acid  radicals  are  first  substituted  for  the  halogen, 
and  these  compounds  are  hydrolyzed.  2.  Another  method  of 
formation  is  by  first  forming  a  compound  containing  one  hy^ 
droxyl  group  and  chlorine,  a  chlorhydin,  through  the  union  of  an 
ethylene  hydrocarbon  and  hypochlorous  acid: 

CH2:CH2  +  HOC1  =  CH2C1.CH2OH 

Glycol 
chlorhydrin 

and  then  replacing  the  chlorine  with  hydroxyl  by  means  of  moist 
silver  oxide: 

CH2C1.CH2OH  +  AgOH  =  CH2OH.CH2OH  +  AgCl 

3.  The  glycols  are  also  formed  by  the  oxidation  of  olefines  by 
means  of  an  alkaline  solution  of  potassium  permanganate  or  by 
hydrogen  dioxide: 

CH2:CH2  +  O  +  H2O  =  CH2OH.CH2OH 


I$7  POLYHYDROXYL  ALCOHOLS 

4.  Diamines  are  converted  into  glycols  by  nitrous  acid  (cf.  p.  131), 
CH2.NH2.HNO2       CH2OH 

CH2.NH2.HNO2      CH2OH 

Properties. — Ethylene  glycol  is  typical  of  all  the  glycols,  and 
will  be  alone  described.  It  is  an  oily,  sweetish  liquid,  which  like 
most  hydroxyl  compounds  is  soluble  in  water  and  only  slightly 
soluble  in  ether.  It  boils  at  195°.  Its  chemical  reactions  are 
those  of  a  double  primary  alcohol.  Thus  its  hydroxyl  hydrogen  is 
replaceable  by  sodium,  and  its  hydroxyl  groups  by  halogens  by 
means  of  phosphorus  halides  or  halogen  acids;  it  forms  single  and 
double  esters  with  inorganic  and  organic  acids,  and  its  alcohol 
groups  are  oxidized  to  aldehyde  and  acid  groups,  with  the  final 
production  of  oxalic  acid  before  breaking  down  into  carbon 
dioxide  and  water.  When  the  higher  glycols  contain  secondary  or 
tertiary  alcohol  groups,  their  behavior  on  oxidation  is  in  part  that 
of  secondary  or  tertiary  alcohols. 

Alkylene  Oxides. — Closely  related  to  the  glycols  are  the  alkyl- 
ene  oxides,  which  may  be  regarded  as  glycols  from  which  the 
elements  of  water  have  been  subtracted.  This  cannot,  however, 
be  directly  accomplished  in  most  cases,  but  the  compounds  may 
be  made  by  the  action  of  potassium  hydroxide  on  the  correspond- 
ing chlorhydrines: 

CH,. 
CH2C1.CH2OH  +  KOH  =    j        >O  +  KC1  +  H2O 

CH/ 

Alcohols  with  More  than  Two  Hydroxyl  Groups 

Derivatives  of  the  paraffins  containing  four,  five,  six,  and 
seven  hydroxyl  groups  are  known.  Certain  hexahydroxyl 
alcohols  occur  in  the  sap  of  various  trees;  mannitol  or  manna, 
CH2OH(CHOH)4CH2OH,  being  obtained  from  the  mountain  ash. 
As  the  number  of  hydroxyl  groups  increases,  the  compounds  are 
sweeter  and  become  more  like  sugars,  to  which  they  are  closely 


INTRODUCTION  TO   ORGANIC   CHEMISTRY  158 

related;  and  the  tendency  to  decompose  when  heated,  with  the 
loss  of  the  elements  of  water,  becomes  greater.  Among  the  poly- 
hydroxyl  alcohols  the  only  one  of  practical  importance  is  that 
commonly  known  as  glycerine  or  glycerol 

Glycerol,  CH2OH.CHOH.CH2OH,  or  "glycerine,"  is  the  sim- 
plest possible  trihydroxyl  alcohol.  It  may  be  formed  by  methods 
like  those  used  for  the  formation  of  glycol;  and  is  produced  in 
large  quantities  from  fats  (which  are  glyceryl  esters  of  certain  of 
the  higher  paraffin  or  fatty  acids)  by  replacement  of  the  acid  radi- 
cals with  hydroxyl.  This  is  effected  by  alkali  hydroxides  with 
the  production  of  soap  (p.  109)  and  glycerol,  or  by  the  action  of 
superheated  steam,  when  the  products  are  glycerol  and  the  fatty 
acids.  The  watery  liquid  containing  the  glycerine  is  purified  by 
filtration  through  animal  charcoal  and  the  water  removed  by  evapo- 
ration in  a  partial  vacuum.  The  product,  which  is  still  impure, 
is  refined  for  medical  purposes  and  for  making  nitroglycerine,  by 
distillation  in  a  current  of  superheated  steam,  and  treatment  again 
with  animal  charcoal.  It  is  finally  concentrated  in  a  vacuum. 
Glycerine  is  always  formed  in  small  amounts  in  the  alcoholic 
fermentation  of  sugars,  so  that  it  is  present  in  all  undistilled 
alcoholic  beverages. 

Glycerol  is  a  syrupy  liquid,  colorless  and  odorless,  heavier  than 
water  (specific  gravity  1.265  at  15°),  miscible  with  water  or  alco- 
hol in  all  proportions,  but  insoluble  in  ether  and  chloroform.  It 
boils  at  290°  with  very  slight  decomposition.  It  dissolves  many 
inorganic  and  organic  substances.  It  is  very  hygroscopic,  and 
this  property  together  with  its  non-volatility  leads  to  an  extensive 
use  in  non-drying  Inks,  such  as  copying  inks  and  those  employed 
on  typewriter  ribbons  and  the  pads  for  rubber  stamps.  Other 
uses  are  in  pharmacy,  in  the  preparation  of  tobacco,  in  confec- 
tionery, preserves,  and  cosmetics;  but  the  largest  amount  is 
employed  in  making  "nitroglycerine." 

The  formula  given  to  glycerol  is  the  only  one  that  can  explain 
the  methods  of  its  formation  and  the  products  which  are  obtained 


159  POLYHYDROXYL  ALCOHOLS 

from  it  in  various  reactions.  Its  oxidation  products  show  the 
presence  of  two  primary  and  one  secondary  alcohol  groups.  On 
heating  glycerol  with  dehydrating  substances,  (P2Os)  acrolein  is 
formed  (p.  86).  Glycerol  can  undergo  fermentation,  and  yields 
different  products  according  to  the  nature  of  the  ferment.  One 
bacillus  converts  it  chiefly  into  butyl  alcohol,  which  is  often  pre- 
pared in  this  way. 

Glycerol,  like  all  alcohols,  forms  esters  with  acids,  and  since  it 
contains  three  hydroxyl  groups,  it  can  form  three  different  esters 
with  a  monobasic  acid,  according  as  one,  two,  or  all  three  of  the 
hydroxyls  are  replaced  by  acid  radicals.  The  most  important  of 
its  esters  are  those  that  occur  in  the  natural  fats  and  oils  (p.  160) 
and  nitroglycerine. 

Nitroglycerine  is  the  common  name  of  the  trinitrate  of  glycerol, 
CH2(O.NO2).CH(O.NO2).CH2(O.NO2),  and  is  not  a  nitro-com- 
pound  as  the  name  implies.  It  is  made  by  adding  glycerine  slowly 
to  a  well-cooled  mixture  of  concentrated  nitric  and  sulphuric 
acids,  so  long  as  it  dissolves.  On  pouring  the  solution  thus 
obtained  into  a  large  quantity  of  water,  the  nitroglycerine  sepa- 
rates, as  a  heavy  oil.  It  is  thoroughly  washed  with  a  solution  of 
sodium  carbonate  to  remove  all  acid,  and  then  with  water,  and 
finally  dried  by  chloride  of  calcium.  Pure  nitroglycerine  is  color- 
less and  odorless.  Its  specific  gravity  is  1.6  at  15°.  It  is  almost 
insoluble  in  water  but  dissolves  somewhat  in  alcohol  and  mixes  in 
every  proportion  with  ether,  chloroform  and  benzene.  A  com- 
parison of  its  solubility  with  that  of  glycerol  is  a  good  illustration 
of  the  influence  of  hydroxyl  groups  on  this  property.  Nitrogly- 
cerine is  poisonous,  but  is  a  valuable  remedy  in  heart  disease.  It 
is  saponified  by  caustic  alkalies,  but  the  reaction  is  accompanied  by 
the  production  of  some  oxidation  products  of  glycerol  and  reduc- 
tion of  the  alkali  nitrate  to  nitrite.  Pure  nitroglycerine  keeps 
without  change,  but  if  impure,  it  slowly  decomposes.  Hence  it  is 
important  to  use  pure  glycerol  in  its  manufacture,  and  to  remove 
from  it  all  traces  of  acid.  Nitroglycerine  is  best  known  as  a  pow- 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  l6o 

erful  explosive.  It  is  used  largely  in  the  form  of  "dynamite," 
which  is  nitroglycerine  absorbed  in  infusorial  earth  or  some  other 
substances.  By  this  device  it  is  brought  into  solid  form  which  can 
be  conveniently  used.  The  most  powerful  dynamite  contains 
75  per  cent,  of  nitroglycerine.  It  is  also  converted  into  a  jelly- 
like  solid  by  dissolving  in  it  a  small  quantity  (7-8  per  cent.)  of 
gun-cotton  (p.  223),  and  in  this  form  is  known  as  "  explosive  gel- 
atine." Small  amounts  of  nitroglycerine  may  be  kindled  without 
exploding,  and  considerable  quantities  of  dynamite  burn  quietly. 
Dynamite  is  not  very  sensitive  to  shocks,  and  is  transported  with 
little  danger,  but  nitroglycerin  is  readily  exploded  by  shock.  All 
forms  are  exploded  by  a  detonating  substance  such  as  mercury 
fulminate  (p.  151),  which  is  usually  "fired"  by  electricity. 

Natural  Oils  and  Fats. — Besides  the  petroleum  oils,  whose  origin 
is  still  in  question,  and  ozokerite  or  earth  wax,  there  are  many  oils 
and  fats  and  a  few  waxes  that  are  obtained  from  plants  and  ani- 
mals. Two  classes  of  oils  are  recognized :  the  fixed  or  fatty  oils 
and  the  essential  oils.  The  essential  oils  are  practically  all  of 
vegetable  origin,  and  are  characterized  by  strong  and  individual 
odors.  They  can  usually  be  distilled  without  decomposition  and 
evaporate  from  paper  without  leaving  a  permanent  oily  stain. 
Most  of  them  are  not  sensibly  soluble  in  water  but  impart  to  it 
their  characteristic  odors.  Their  composition  is  very  varied, 
including  hydrocarbons  such  as  cymene,  pinene  (in  turpentine 
oil),  camphene,  and  limonene;  alcohols — benzyl  alcohol  in  balsam 
of  Peru  and  menthol  in  peppermint  oil;  phenols — thymol  in  oil 
of  thyme;  esters  of  acetic,  butyric,  valeric,  benzoic,  salicylic,  and 
and  other  acids;  many  aldehydes  such  as  benzaldehyde  in  oil  of 
bitter  almonds,  cinnamic  aldehyde  in  cinnamon  oil)  and  vanillin 
(p.  347)  in  vanilla;  ke tones  such  as  camphor;  and  others. 

The  fixed  oils  and  fats  are  insoluble  in  water,  leave  a  permanent 
oily  stain  on  paper,  and  decompose  when  heated,  giving  acrolein 
(p.  86)  as  one  of  the  decomposition  products.  They  are  found 
in  both  plants  and  animals,  and  most  commonly  consist  of  tri- 


l6oa  POLYHYDROXYL  ALCOHOLS 

glyceryl  esters  of  organic  acids.  The  esters  most  frequently 
present  are  the  glycerides  of  palmitic,  stearic,  and  oleic  acids, 
known  as  palmitin,  stearin,  and  ole'in.  The  first  two  of  these 
esters  are  solids  and  ole'in  a  liquid;  and  when  these  three  are 
the  principal  constituents — as  is  the  case  with  many  of  the 
animal  fats  especially,  their  proportions  determine  the  con- 
sistency of  the  fat.  Thus,  olive  oil  contains  about  75  per  cent, 
of  ole'in;  lard  which  melts  at  35°-38°,  about  60  per  cent.;  and 
tallow,  melting  at  47°-48°,  about  25  per  cent.  Among  the  con- 
stituents of  some  of  the  fats  and  oils  are  also  glyceryl  esters  of 
a  number  of  other  fatty  acids,  such  as  butyric,  caproic,  caprylic, 
lauric,  and  myristic  of  the  saturated  series;  cro tonic,  physetoleic, 
and  ricilinoleic  (hydroxyoleic)  of  the  oleic  series;  linolic,  an  acid 
with  two  double  bonds;  linolenic  and  isolinolenic  (p.  112),  acids 
with  three  double  bonds. 

Butter  fat  differs  from  all  other  fats  and  oils  by  containing  about 
7.7  per  cent,  of  triglyceryl  butyratein  addition  to  stearin,  palmitin, 
ole'in,  and -traces  of  other  glyceryl  esters. 

Oils  like  linseed  oil,  that  consist  chiefly  of  glycerides  of  the  highly 
unsaturated  acids,  linolic,'  linolenic,  and  isolinolenic,  are  called 
"drying"  oils  because  they  absorb  oxygen  from  the  air  and  be- 
come dry  and  hard.  Such  oils,  on  this  account,  are  extensively 
used  in  paints  and  varnishes.  Linseed  oil  dries  more  rapidly  if  it 
has  been  "boiled,"  a  process  in  which  the  oil  is  heated  to  about 
150°  with  certain  oxides  or  salts  such  as  litharge  or  borate  of 
manganese  that  are  called  "driers"  and  probably  act  as  contact 
agents.  Much  heat  is  developed  in  the  drying  of  these  oils  and 
occasions  the  danger  of  spontaneous  combustion  in  the  oily  rags 
and  waste  used  by  painters. 

Some  oils,  such  as  cotton  seed  oil,  that  con  tain  small  amounts  of 
linolic  acid  ester  are  semi-drying,  while  many  such  as  olive  and 
rape  oils  are  non-drying.  These  oils  generally  become  rancid 
from  exposure  to  air,  apparently  because  of  a  partial  hydrolysis 
occasioned  by  bacterial  action  followed  by  oxidation  of  the  fatty 
acids  that  are  set  free. 


INTRODUCTION    TO    ORGANIC   CHEMISTRY  l6ob 

In  the  last  few  years  the  production  of  "hardened"  oils  has 
developed  into  an  industry  of  considerable  importance.  The 
chemical  change  involved  consists  in  "  hydrogenation "  or~  addi- 
tion of  hydrogen  to  the  unsaturated  esters  in  the  oils,  by  which 
they  are  converted  into  saturated  compounds.  The  reaction  is 
effected  by  leading  hydrogen  into  the  moderately  heated  oil  after 
the  addition  of  a  substance  that  acts  as  a  catalyst.  The  most 
important  of  these  catalysts  is  finely  divided  nickel  (Sabatier  and 
Senderens),  though  palladium,  platinum,  and  other  metals  are 
also  employed.  A  large  variety  of  oils  can  be  thus  hardened — 
vegetable,  animal,  train,  fish,  and  whale  oils — and  the  resulting 
fats  are  of  great  commercial  importance,  being  largely  used  in 
soap  and  candle  making,  and  also  providing  edible  fats  from  oils. 
One  of  the  latter  products  is  "crisco,"  a  substitute  for  lard. 

A  method  of  saponifying  fats  for  soap-making  has  recently  been 
introduced  into  the  industry  by  Twitchell,  in  which  an  aromatic 
sulphonic  acid  acts  as  a  catalyzer.  The  exact  nature  of  the  com- 
pound is  not  disclosed,  but  it  is  prepared  by  the  action  of  sulphuric 
acid  on  a  solution  of  olei'c  acid  in  an  aromatic  hydrocarbon:  and 
1-2  per  cent,  of  it  is  effective  in  producing  saponification. 


CHAPTER  XIII 

OXIDATION  DERIVATIVES  OF  POLYHYDROXYL 
ALCOHOLS 

A  large  number  of  compounds  may  be  regarded  as  oxidation 
derivatives  of  the  alcohols  discussed  in  the  last  chapter.  The 
compounds  may  contain  unchanged  alcohol  groups  —  primary, 
secondary,  and  tertiary  —  with  aldehyde  groups,  ketone  groups, 
or  carboxyl  groups,  in  every  possible  combination.  From  glycol, 
for  example,  the  derivatives  are: 

CH2OH    CH2OH      CH2OH      CHO       CHO  CO.OH 


CH2OH  CHO     CO.OH   CHO   CO.OH   CO.OH 

m»,™i        Glycollic  Glycollio        purrivQi  Glyoxylic  Oxalic 

G1yco1       aldehyde  acid  Glyoxal  ad(f  &cid 

From  glycerol  and  the  higher  polyhydroxyl  alcohols  ketone 
derivatives  may  also  be  obtained  such  as  dihydroxy-acetone, 
CH2OH.CO.CH2OH. 

But  while  many  of  these  substances  are  formed  by  the 
actual  oxidation  of  the  corresponding  glycols,  etc.,  this 
method  is  not  often  used  for  their  preparation,  because  of 
the  difficulty  of  controlling  the  reaction  so  as  to  obtain  a  good 
yield  of  the  individual  products.  Glyceric  acid  is,  however, 
usually  made  by  oxidizing  glycerol  with  nitric  acid,  but,  in 
general,  the  compounds  which  form  the  subject  of  this  chapter 
are  prepared  by  indirect  methods. 

The  student  will  recall  that  the  most  important  general  methods 
for  the  introduction  of  the  hydroxyl  groups  are:  By  replacement 
of  a  halogen  atom  through  the  action  of  water,  alkali  hydroxide, 
or  silver  hydroxide;  by  saponification  of  an  ester;  for  a  primary 

161 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  162 

alcohol  group,  the  reaction  of  nitrous  acid  on  a  primary  amine 
group,  and  for  a  secondary  alcohol  group,  the  reduction  of  a 
carbonyl  group.  For  the  general  methods  of  introducing  the 
aldehyde,  ketone,  (CO),  and  carboxyl  groups,  reference  should  be 
made  to  the  methods  of  forming  aldehydes,  ketones  and  acids. 

Aldehyde-alcohols  and  Ketone-alcohols 

The  simpler  compounds  of  these  classes  are  of  interest  chiefly 
because  of  the  fact  that  some  of  the  sugars  are  aldehyde  or  ketone- 
alcohols,  while  other  so-called  carbohydrates  are  converted  into 
aldehyde  or  ketone-alcohols  by  hydrolysis.  The  carbohydrates 
themselves  form  the  subject  of  a  separate  chapter.  Only  a  few 
of  the  simpler  aldehyde-alcohols  and  ketone-alcohols  have  been 
made,  and  these  are  of  no  especial  practical  importance. 

Glycollic  aldehyde,  CH2(OH).CHO,  or  hydroxy-acetaldehyde,  is 
formed  in  the  oxidation  of  glycol.  It  can  be  prepared  from  acetal, 
CH3.CH(OC2H5)2,  by  appropriate  reactions.  Chlorine  is  sub- 
stituted in  the  CH3  group,  and  replaced  by  hydroxyl,  making 
CH2OH.CH(OC2H5)2;  and  then  by  the  action  of  a  dilute  acid, 
this  glycolacetal  is  hydrolyzed  into  glycollic  aldehyde  and  alcohol 
(cf.  p.  79).  It  is  known  only  in  solution.  Its  aldehyde  character 
is  marked.  It  reduces  Fehling's  solution  at  room  temperature,  is 
colored  yellow  when  heated  with  alkalies,  and  is  oxidized  by 
bromine  water  to  glycollic  acid.  On  standing  at  o°  with  dilute 
alkali  it  suffers  "condensation"  like  that  of  acetaldehyde,  with 
the  formation  of  a  tetrose,  CH2(OH).CH(OH).CH(OH).CHO. 

Aldol  or  fchydroxybutyric  aldehyde,  CH3.CH(OH).CH2.CHO, 
is  formed  by  the  polymerization  of  acetaldehyde  (p.  82),  and  was 
the  first  known  case  of  this  characteristic  aldehyde  reaction 
f "  aldol  condensation  ") . 

Ketoles. — A  number  of  compounds  with  a  ketone  group 
and  a  hydroxyl  group  are  known,  such  as  hydroxyl  acetone 
or  acetocarbinol,  CH3.CO.CH2(OH),  and  acetobutyl  alcohol, 
CH3.CO.(CH2)3.CH2(OH). 


163  DERIVATIVES   OF  POLYHYDROXYL  ALCOHOLS 

Dialdehydes  and  Diketones 

CHO 

Glyoxal,    |        ,  is  one  of  the  several  products  formed  by  the 

CHO 

oxidation  of  glycol  or  ethyl  alcohol  or  aldehyde  with  nitric  acid. 
A  solution  of  it  may  be  prepared  in  this  way  from  aldehyde  or 
paraldehyde,  and  on  evaporation  the  glyoxal  is  obtained  as  an 
amorphous,  hard  mass,  not  entirely  free  from  water.  Its  aldehyde 
character  is  shown  by  the  formation  of  a  silver  mirror  with  am- 
moniacal  silver  nitrate,  and  the  presence  of  two  aldehyde  groups 
by  the  composition  of  the  crystalline  addition  products  with  acid 
sodium  sulphite.  By  dilute  alkalies  it  is  converted  into  a  glycollic 
acid  salt,  CH2(OH).CO.ONa,  one  aldehyde  group  being  reduced, 
and  the  other  oxidized. 

Acetonylacetone,  CH3.CO.CH2.CH2.CO.CH3,  is  an  example 
of  a  diketone,  which  may  be  regarded  as  an  oxidation  product 
of  a  7-hexylene  glycol.  It  is  made,  however,  in  an  indirect 
way.  It  is  a  liquid  of  pleasant  odor,  which  boils  at  194°. 

Aldehyde -ketones 

The  simplest  representative  of  this  class  is  the  methylglyoxal, 
CH3.CO.CHO,  and  may  be  looked  on  as  a  derivative  of  propylene 
glycol. 

Alcohol-acids 

Carbonic  acidt  HO.CO.OH,  may  be  considered  as  hydroxy- 
formic  acid.  It  and  its  derivatives  will  be  discussed  later. 

Glycollic  acid,  CH^OH.CO.OH,  or  hydroxyacetic  acid,  is  (with 
the  exception  of  carbonic  acid)  the  simplest  of  these  compounds. 
Its  structure  is  shown  by  its  formation  from  monochloracetic  acid, 
when  this  is  boiled  with  water: 

CH2C1.CO.OH  +  HOH  -»  CH2OH.CO.OH 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  164 

It  occurs  in  unripe  grapes.  It  is  formed  by  the  oxidation  of 
glycol  or  of  ethyl  alcohol  with  nitric  acid,  by  reduction  of  oxalic 
acid,  and  by  the  action  of  dilute  alkalies  on  glyoxal  (p.  163.) 
Glycollic  acid  is  a  crystalline  substance,  which  melts  at  80°  and 
dissolves  readily  in  water.  Nitric  acid  converts  it  into  oxalic 
acid. 

Hydroxypropionic  Acids. — There  are  two  chemically  different 
acids  of  this  name  whose  formulas  are,  CH3.CHOH.CO.OH, 
and  CH2OH.CH2.CO.OH.  They  may  be  made  from  other 
compounds  such  as  iodo-  or  amino-propionic  acids  by  the  usual 
methods  of  hydroxyl  substitution.  That  they  are  monobasic 
acids  is  proved  by  the  composition  of  their  salts;  and  that  they 
contain  one  hydroxyl  in  addition  to  that  of  the  carboxyl,  is  shown 
by  the  fact  that  sodium  acts  on  them  with  the  formation  of  com- 
pounds in  which  it  takes  the  place  of  two  hydrogen  atoms — those 
of  the  hydroxyl  and  carboxyl  group.  Both  acids  form  thick,  sour 
syrups.  Their  diversity  is  shown  by  a  great  difference  in  the 
solubility  of  their  zinc  salts,  and  by  the  following  reactions  which 
serve  to  decide  which  of  the  two  formulas  represents  the  structure 
of  each.  One  of  them  when  oxidized  with  potassium  permanga- 
nate is  converted  into  a  ketone  acid,  acetylformic  acid,  CH3.CO.- 
CO.OH.  This  result  is  evidence  of  the  presence  of  a  secondary 
alcohol  group  in  the  acid,  the  reaction  being: 

CH3.CHOH.CO.OH  +  O  =  CH3.CO.CO.OH  +H2O 
The  formula  given  the  acid  in  this  equation  is  also  indicated  by 
the  fact  that  when  heated  with  dilute  sulphuric  acid,  it  breaks  up 
into  aldehyde  and  formic  acid,  a  reaction  which  is  characteristic 
of  many  a-hydroxy  acids: 

CH3.CHOH.CO.OH  =  CH3.CHO  +  HCO.OH 
and  that  its  nitrile  may  be  made  by  direct  combination  of  aldehyde 
and  hydrocyanic  acid: 

CH3.CHO  +  HCN  =  CH3.CHOH.CN 
This  acid  is,  therefore,  a-hydroxypropionic  acid. 


165  DERIVATIVES   OF  POLYHYDROXYL   ALCOHOLS 

The  other  must,  then,  be  /3-hydroxypropionic  acid,CH2  OH.- 
CH2.CO.OH;  and  this  formula  is  confirmed  by  its  oxidation  into 
the  corresponding  dibasic  malonic  acid,  CO.OH.CH2.CO.OH, 
showing  the  presence  of  a  primary  alcohol  group;  and  also  by  its 
breaking  up  when  heated  into  the  unsaturated  acrylic  acid, 
CH2:CH.CO.OH  (p.  no). 

a-Hydroxypropionic  acid,  CH3.CHOH.CO.OH,  is  the  acid  of 
sour  milk,  being  formed  by  the  action  of  certain  bacteria  on  the 
milk  sugar.  Hence  it  is  known  as  lactic  acid.  (Tablets  contain- 
ing pure  cultures  of  lactic  acid  bacteria  are  sold  under  the  name 
of  "lactone"  or  "butter-milk  tablets.")  Lactic  acid  is  also  the 
product  of  special  fermentations  of  other  sugars,  and  is  found  in 
"sauerkraut"  and  in  the  gastric  juice,  and  is  present  in  "beef- 
extract."  But  the  lactic  acid  obtained  from  the  last  source 
differs  from  that  from  most  other  sources  and  from  the  synthetic 
lactic  acid,  by  being  "optically  active;"  that  is,  its  solutions 
rotate  the  plane  of  polarized  light.  On  fermentation  of  cane-sugar 
by  means  of  a  special  culture  of  bacteria,  an  active  lactic  acid  is 
formed  which  also  rotates  the  plane  of  polarized  light,  but  in  the 
opposite  direction  from  that  which  is  made  from  beef-extract. 
The  latter  turns  the  plane  to  the  right,  the  former  to  the  left. 
The  salts  of  these  two  acids  give  optically  active  solutions  which 
rotate  the  plane  in  a  sense  opposite  to  the  rotation  by  the  respec- 
tive acids.  The  ordinary  salts  of  both  these  acids  have  the  same 
solubility,  but  the  strychnine  salt  of  the  levo-rotatory  acid  is  less 
soluble  than  that  of  the  dextro-rotatory,  and  from  a  solution 
of  the  strychnine  salt  of  the  ordinary  lactic  acid,  which  is  "inac- 
tive," two  lots  of  crystals  can  be  obtained  by  fractional  crystal- 
lization, and  from  these  the  two  optically  active  acids  may  be  set 
free.  The  dextro-acid  may  be  also  made  from  the  ammonium 
salt  of  the  inactive  acid  by  means  of  a  mould,  penicillium  glaucum, 
which  destroys  the  levo  form.  Special  ferments  determine  the 
formation  from  sugars  of  one  or  the  other  of  the  active  acids. 
When  the  zinc  salts  of  the  two  active  acids  in  solution  are  mixed 


INTRODUCTION  TO   ORGANIC   CHEMISTRY  1 66 

in  equal  proportions,  the  less  soluble  salt  of  the  inactive  acid 
crystallizes  out.  It  appears,  therefore,  that  the  inactive  acid  is  a 
mixture  in  equal  parts  of  the  two  oppositely  active  acids.  The 
three  acids  differ  in  no  chemical  way,  and  this  "physical  isomerism" 
which  is  found  cannot  be  represented  by  such  structural  formulas 
as  we  have  thus  far  employed.  A  satisfactory  explanation  is, 
however,  found  in  formulas  which  give  arrangements  of  atoms 
and  groups  in  space  of  three  dimensions,  instead  of  the  representa- 
tions in  a  single  plane  such  as  have  served  in  our  discussions  up  to 
this  point. 

Stereochemistry 

In  methane  we  saw  that  each  of  the  four  hydrogen  atoms  bore 
the  same  relation  to  the  other  three  and  to  the  carbon  atom;  at 
least,  it  has  not  proved  possible  to  make  different  monosubsti- 
tution  products  of  methane.  This  symmetry  of  the  methane 
molecule  is  satisfactorily  indicated  by  the  usual  plane  graphic  for- 
H 

mula,  H — C — H.     If  chlorine  replaces  any  one  of  the  hydrogen 

H 

atoms,  we  have  formulas  which  may  be  considered  identical.  B  ut 
when  two  atoms  of  hydrogen  are  replaced  there  are  two  formulas 
possible  which  are  not  strictly  identical  in  this  mode  of  representa- 
tion; for  in  one  the  hydrogen  and  chlorine  atoms  alternate  as  we 
go  round  the  carbon  atom,  and  in  the  other  the  two  chlorine  atoms 
are  next  each  other : 

H  H 

Cl— C— Cl  and  H— C— Cl 

I  I 

H  Cl 

And  yet  only  one  dichlormethane  has  ever  been  obtained. 
Such  differences  in  arrangement  have  been  hitherto  disregarded 


i67 


DERIVATIVES   OF  POLYHYDROXYL  ALCOHOLS 


in  our  discussions.  The  phenomena  of  optical  activity  or  physical 
isomerism,  however,  has  led  to  the  development  of  spatial  repre- 
sentations, which  account  for  the  existence  of  but  one  dichlor- 
methane  and  other  similar  failures  of  the  plane  formula;  and  also 
gives  a  good  explanation  of  the  facts  of  optical  activity.  There  is, 
of  course,  every  reason  to  believe  that  the  molecular  arrangement 
is  never  confined  to  bi-dimensional  space,  but  that  the  atoms  and 
groups  form  tri-dimensional  structures;  and  the  graphic  formulas 
have  been  regarded  as  giving  merely  a  plan  or  diagram  with  no 
attempt  to  represent  the  actual  relative  positions. 

The  tetrahedron,  the  simplest  regular  solid,  is  the  only  form  that 
can  give  full  expression  to  the  symmetry  of  methane,  and  this  was 
taken  by  Van't  Hoff  andLe  Bel  as  the  basis  for  their  formulation  of 
spatial  relations.  The  carbon  atom  is  placed  at  the  center  of  the 
tetrahedron,  its  four  valencies  being  directed  to  the  four  solid 
angles. 


H 


ci 

2.  Monochlormethane 

H 


3.  Dichlormethane 


4.  Dichlormethane 


The  diagrams  show  the  tetrahedral  formulas  for  methane,  mono- 
chlormethane,  and  dichlormethane.  They  are  all  symmetrical, 
and  formulas  3  and  4  are  identical;  for  3  may  readily  be  turned  so 


INTRODUCTION   TO    ORGANIC   CHEMISTRY 


168 


that  the  chlorine  and  hydrogen  atoms  coincide,  or,  in  other  words, 
the  two  figures  are  superposable. 

This  symmetry  holds  good  for  all  compounds  in  which  a  carbon 
atom  is  combined  with  four  elements  or  groups  of  the  same  kind, 
or  any  combination  of  elements  or  groups  except  that  of  four  differ- 
ent ones.  In  this  case  there  are  possible  two  arrangements  which 
are  unsymmetric  or  asymmetric  and  which  cannot  be  turned  into 
coincidence  or  superposed.  On  this  account,  a  carbon  atom 
united  to  four  different  atoms  or  groups  is  called  an  asymmetric 
carbon  atom.  ,The  two  asymmetric  arrangements  bear  the  rela- 
tion to  each  other  of  an  object  and  its  image  in  a  plane  mirror,  as 
may  be  seen  by  study  of  the  diagrams,  or  better  by  tetrahedral 
forms. 


The  relations  shown  in  the  tetrahedral  formulas  may  also  and 
more  conveniently  be  indicated  by  formulas  like  those  below, 
which  are  projections  of  the  tri-dimensional  arrangements  on  the 
plane  of  the  paper: 

a  a 

i          i 

d— C— b    b— C— d 

I  I 


It  will  be  noticed  that  the  configurations  cannot  be  made  to  coin- 
cide by  turning  one  of  them  in  the  plane  of  the  paper.  This  will 
be  found  true  of  all  such  projections  of  asymmetrical  tetrahedral 
formulas,  and  we  shall  make  use  of  this  mode  of  representation  in 
future  instances  of  physical  isomerism. 

By  these  formulas,  we  have  a  means  of  recording  the  physical 


169 


DERIVATIVES   OF  POLYHYDROXYL  ALCOHOLS 


difference  which  we  are  discussing,  while  the  chemical  identity 
is  still  preserved. 

A  large  number  of  optically  active  organic  substances  is  known. 
When  the  plane  of  polarized  light  is  rotated  on  passing  through  a 
solid  substance,  it  can  be  assumed  that  the  effect  is  due  to  the 
arrangement  of  the  molecules,  as  in  the  various  crystal  forms; 
but  in  the  case  of  the  lactic  acids  and  other  so-called  optically 
active  chemical  compounds,  the  activity  is  shown  in  solution, 
where  free  motion  of  the  molecules  is  probable,  and  where  they 
certainly  do  not  assume  any  fixed  relations  to  each  other;  and 
camphor  and  certain  terpenes  retain  their  optical  activity  unim- 
paired in  the  state  of  vapor.  In  all  the  optically  active  compounds, 
we  find  on  examining  their  ordinary  structural  formulas  that  there 
is  an  asymmetric  carbon  atom. 

In  lactic  acid,  CH3.CH(OH).CO.OH,  the  four  different  groups 
CH3,  H,  OH,  and  CO. OH  are  in  combination  with  the  carbon 
atom  which  is  printed  in  blacker  type.  The  formulas  of  the  two 
optically  active  lactic  acids  are: 


CO.OH 


CO.OH 


or 


d-Lactic  acid 

CO.OH 

H— C— OH 
CH3 


The  choice  of  one  formula  rather  than  the  other  to  represent  the 
dextro-  or  levo-compound  is  arbitrary. 

When  a  compound  contains  an  asymmetric  carbon  atom,  and 
is  optically  inactive,  the  explanation  is  that  equal  amounts  of  the 


INTRODUCTION  TO   ORGANIC   CHEMISTRY  170 

two  oppositely  active  substances  are  probably  present:  and  this, 
as  we  have  seen,  agrees  with  the  facts  which  have  been  stated  as 
to  the  separation  and  the  mixing  of  the  two  active  lactic  acids. 
In  case  of  compounds  with  two  asymmetric  carbon  atoms,  as  in 
mesotartaric  acid  (p.  193),  the  optical  inactivity  may  be  due  to 
a  different  cause. 

Optically   active    compounds    which   have   been   previously 


3v 

mentioned  are:  active  amyl  alcohol,  ^>CH.CH2OH  (p.  67), 

C2H/ 
and   one   of   the   four   valeric    acids   (p.    108)    which  has   the 


av 
formula,  ^>CH.CO.OH.      Each  formula  contains  an  asynv 

C2H/ 

metrical  carbon  atom.  The  active  alcohol  from  fermentation 
is  levo-rotatory;  on  oxidation  it  yields  dextro-rotatory  valeric 
acid.  An  inactive  modification  of  the  acid  has  been  synthe- 
sized, and  resolved  by  its  brucine  salts  into  dextro  and  levo 
components. 

It  is  of  great  interest  to  note  that  this  theory  of  the  relation  of 
optical  activity  to  the  asymmetric  tetravalent  carbon  atom  has 
been  found  to  explain  in  a  similar  manner  the  phenomena  of 
optical  activity  recently  discovered  in  compounds  of  other 
tetravalent  elements.  These  are  compounds  of  tetravalent  tin, 
silicon,  sulphur,  and  selenium,  in  all  of  which  four  different  groups 
or  atoms  are  directly  united  to  these  elements,  and  can  be  repre- 
sented as  tetrahedral  arrangements. 

Lactic  acid  is  made  commercially  by  fermentation  of  sugar,  and 
is  used  in  dyeing  and  calico  printing  as  a  substitute  for  tartaric 
and  citric  acids,  and  its  antimony  salt  is  used  in  place  of  tartar 
emetic  as  a  mordant. 

The  lactic-acid  fermentation  is  often  induced  in  making  grain 
alcohol,  as  a  i  per  cent,  solution  of  the  acid  inhibits  the  action 
of  other  bacterial  ferments,  while  having  little  effect  on  yeast. 

When  distilled,  lactic  acid  is  decomposed  into  aldehyde,  water, 
carbon  monoxide  and  other  products.  Since  lactic  acid  is  both  an 


1 71  DERIVATIVES   OF   POLYHYDROXYL  ALCOHOLS 

alcohol  and  an  acid,  two  molecules  of  it  may  react  to  form  an 

xO.OC.CHOH.CH3 
ester,     CH3.CH  ^  ,     and  this  by  a  second 

\CO.OH 
reaction  of  the  same  kind  may  give  a  compound  called  lactide 

xO.OC.CH.CHa 
and  having  the  constitution   CH3.CH  <^          /  .      The 


\co.o 


lactide  is  formed  when  the  acid  is  heated  to  150°  in  a  current  of 
dry  air.  Lactide  is  an  indifferent  substance,  and  in  contact 
with  water  slowly  changes  back  to  lactic  acid. 

0-Hydroxypropionic  acid,  CH2OH.CH2.CO.OH,  is  also  called 
hydracrylic  add,  on  account  of  its  relation  to  acrylic  acid.  To  the 
evidence  for  its  structure  already  given,  may  be  added  the  fact 
of  its  synthesis  from  ethylene  through  ethylene  chlorhydrin. 
Ethylene  unites  directly  with  hypochlorous  acid,  when  led  into 
its  dilute  solution,  giving  ethylene  or  glycol  (chlorhydrin: 

CH,:CH2  +  HOC1  =  CH2OH.CH2C1, 

and  the  chlorhydrin,  which  is  a  liquid,  boiling  at  128°,  reacts 
with  potassium  cyanide  forming  hydracrylic  nitrile,  from  which 
the  acid  is  readily  obtained  by  hydrolysis: 

CH2OH.CH2C1  +  KCN  =  CH2OH.CH2CN  +  KC1 
CH2OH.CH2.CN  +  2H2O  =  CH2OH.CH2.CO.OH  +  NH3 

It  will  be  noticed  that  hydracrylic  acid  contains  no  asymmetric 
carbon  atom". 

Dehydration  of  Hydroxy-acids. — By  this  is  meant  the  removal 
of  the  elements  of  water  from  the  acids.  This  is  readily  effected, 
and  the  nature  of  the  compounds  which  result  depends  on  the 
relative  positions  of  the  hydroxyl  and  carboxyl  groups. 

a-Hydroxy-acids  form  various  complex  compounds  by  the  loss 
of  the  elements  of  water  from  hydroxyl  and  carboxyl  groups, 
and  the  union  of  two  molecular  residues,  as  in  the  case  of  lactic 


INTRODUCTION   TO    ORGANIC    CHEMISTRY  172 

acid  (p.  171).  From  gly collie  acid,  for  example,  the  following 
compounds  have  been  obtained: 

XCH2.CO.OH  XCH2.COV 

o<  a( 

XCH2.CO.OH  XCH2.O 

HO.CH2.COX  XCH2.CO\ 

>0,  0<  >0 

HO.OC.CH/  X)C.CH2/ 

The  last  is  glycollide,  corresponding  to  lactide.  Compounds  of 
this  constitution  have  received  the  general  name  of  lactides. 

When  heated  with  dilute  sulphuric  acid,  a-hydroxy  acids  often 
split  off  formic  acid  (or  its  equivalent,  CO  and  H2O),  as  in  the 
case  of  lactic  acid. 

0-Hydroxy  acids  when  heated  give  unsaturated  acids,  as  in  the 
case  of  hydracrylic  acid  which  produces  acrylic  acid : 

CH2OH.CH2.CO.OH  =  CH2  rCH.CO.OH 

5-  and  y-hydroxy- acids  lose  the  elements  of  water  very  easily 
from  the  hydroxyl  and  carboxyl  groups  of  a  single  molecule, 
forming  lactones: 

CH2OH.CH2.CH2.CO.OH  =  CH2.CH2.CH2.CO 

L    _0-J 

The  tendency  of  the  7-acids  to  form  lactones  is  so  great,  that 
when  the  acids  are  in  solution  it  occurs  in  most  cases  slowly  at 
ordinary  temperature,  and  immediately  on  boiling.  The  y-lac- 
tones  are  neutral  compounds  which  distil  without  decomposition. 
On  boiling  with  water  the  acid  is  reproduced  to  a  small  extent. 

Glyceric  acid,  CH2OH.CHOH.CO.OH,  is  an  example  of  a 
dihydroxy-acid.  It  may  be  made  by  careful  oxidation  of  glycerol, 
preferably  with  nitric  acid.  Its  constitution  as  a  dihydroxy- 
propionic  acid  is  determined  by  its  formation  from  chlorlactic 
acid,  CH2C1.CHOH.CO.OH,  by  reaction  with  silver  hydroxide. 
Glyceric  acid  is  a  thick  syrup  which  mixes  in  all  proportions  with 


173  DERIVATIVES   OF  POLYHYDROXYL  ALCOHOLS 

water  and  alcohol,  but  is  insoluble  in  ether  (alcohol  -hydroxyl 
groups).  It  is  seen  that  this  acid  contains  an  asymmetric  carbon 
atom.  As  usually  prepared  its  solutions  have  no  effect  on  polar- 
ized light;  but  a  special  bacillus  produces  a  dextro-rotatory  acid 
from  it,  and  by  the  action  of  penicillium  glaucum  on  th/e  solutions 
of  the  ammonium  salt  of  the  inactive  acid,  a  levo-rotatory  acid 
may  be  obtained. 

Aldehyde  and  Ketone  Acids 

Glyoxylic  acid,  CHO.CO.OH,  is  the  simplest  aldehyde  acid. 
It  is  a  product  of  the  oxidation  of  alcohol,  glycol,  or  glycollic 
acid  with  nitric  acid,  and  can  be  prepared  from  dichlor  or  dibrom- 
acetic  acid  by  heating  with  water.  It  shows  itself  to  be  an  alde- 
hyde by  its  reducing  power  (being  itself  oxidized  to  oxalic  acid), 
its  reduction  to  glycollic  acid,  and  its  reactions  with  acid  sodium 
sulphite  and  hydroxylamine.  It  forms  a  syrup  from  which 
crystals  separate  on  long  standing.  These  crystals,  however,  do 
not  have  the  composition  of  the  acid,  but  contain  an  additional 
molecule  of  water  which  cannot  be  driven  off  without  decomposi- 
tion of  the  acid.  Its  salts  also,  except  the  ammonium  salt,  con- 
tain water  and  cannot  be  obtained  in  the  anhydrous  condition. 
Consequently  its  composition  is  sometimes  considered  to  be 
CH(OH)2.CO.OH,  analogous  to  that  of  chloral  hydrate  (p.  92). 
But  its  reactions  are  best  explained  by  the  formula  CHO.CO.OH. 

Pyroracemic  acid,  pyruvic  acid,  or  acetyl  formic  acid,  CH3.CO.- 
CO-OH,  is  a  ketone  acid,  which  owes  its  first  name  to  its  forma- 
tion by  heating  racemic  (tartaric)  acid.  This  is  the  usual  way  for 
preparing  it.  The  yield  is  increased  by  distilling  the  acid  with 
acid  potassium  sulphate.  The  structure  of  pyroracemic  acid  is 
evident  from  its  formation  by  oxidizing  lactic  acid: 

CH3.CHOH.CO.OH  +  O  -»  CH3.CO.CO.OH, 

and  also  from  its  production  by  the  following  methods :  from  a 
dibrompropionic  acid,  CH3.CBr2.CO.OH,  by  the  action  of  silver 


INTRODUCTION  TO   ORGANIC   CHEMISTRY  174 

oxide;  and  from  acetyl  chloride  by  means  of  potassium  cyanide, 
and  subsequent  hydrolysis: 

CHs.CO.Ci  +  KCN  =  CHa.CO.CN  +  KC1 
CH3.CO.CN  +  2H2O  =  CH3.CO.COONH4 

Pyroracemic  acid  gives  the  characteristic  reactions  of  a  ketone 
and  of  an  acid.  It  is  a  liquid,  boiling  with  little  decomposition 
at  about  165°,  and  when  frozen  at  a  low  temperature,  melts  at  9°. 

Acetoacetic  acid,  CH3.CO.CH2.CO.OH,  is  not  known  in  the 
anhydrous  condition.  It  may  be  obtained  by  the  evaporation 
of  its  solutions  as  a  syrup,  but  decomposes  when  warmed  to  some- 
what below  1  00°  into  acetone  and  carbon  dioxide. 

Acetoacetic  acid  is  formed  by  the  oxidation  of  butyric  acid  with 
hydrogen  peroxide,  and  is  also  a  product  of  the  oxidation  of  fats 
and  proteins  in  the  body.  By  the  splitting  off  of  carbon  dioxide 
it  is  converted  into  acetone:  CH3.CO.CH2.CO.OH  =  CH3.CO.- 
CH3  +  CO2;  and  in  the  enol  form,  CH3.COH:CH.CO.OH,  0- 
hydroxycrotonic  acid,  is  reduced  to  /3-hydroxybutyric  acid,  CH3.- 
CHOH.CH2.CO.OH.  These  three  substances,  acetoacetic  acid, 
/3-hydroxybutyric  acid,  and  acetone  are  present  in  considerable 
quantities  in  the  urine  in  severe  cases  of  diabetes  mellitus. 

Acetoacetic  ethyl  ester  is  a  more  stable  compound,  and,  as  it 
readily  reacts  with  many  substances,  is  an  important  aid  in  various 
organic  syntheses.  It  is  prepared  by  the  action  of  sodium  on 
ethyl  acetate.  The  reaction  is  believed  to  proceed  in  the  following 
way:  Sodium  acts  first  on  traces  of  alcohol,  which  are  present  in 
the  acetate,  forming  sodium  ethoxide,  and  then  this  forms  an 
addition  product  with  the  acetate: 

X)Na 


CH3.CO.OC2H5  +  C2H5ONa  = 

)C2H5 

This  immediately  reacts  with  another  molecule  of  the  acetate, 
forming  a  sodium  compound  of  acetoacetic  ester,  and  alcohol: 


175  DERIVATIVES   OF  POLYHYDROXYL  ALCOHOLS 

Na 


2H5  +  CH3.CO.OC2H5  = 
\OC2H5 

CH3.C(ONa):CH.CO.OC2H6  +  2C2H5OH 

Finally  on  adding  acetic  acid  to  the  sodium  compound  thus  formed, 
the  ester,  CH3  .  COH  :  CH  .  CO  .  OC2H5  or  CH3  .  CO  .  CH2CO  .  OC2H5, 
is  set  free. 

It  will  be  noticed  that  two  alternate  formulas  have  just  been 
given  for  the  ester.  The  first  is  the  formula  of  an  unsaturated 
hydroxy  ester,  the  second  of  a  saturated  ketone  ester.  The 
explanation  of  its  formation  leads  most  naturally  to  the  first 
formula  and  some  of  its  reactions  accord  with  this  view;  but,  on 
the  other  hand,  many  of  its  reactions  are  those  of  a  ketone  com- 
pound. It  is  probable  that  it  exists  in  both  forms,  and  that  they 
are  both  present  in  varying  proportions  in  it  and  in  its  substitution 
products,  and  change  readily  into  each  other.  We  have  noticed 
before  in  the  acid  amides  a  similar  case,  where  the  compound 
probably  exists  in  two  forms  which  are  structurally  different. 
This  double  behavior  is  found  in  a  number  of  compounds  and  is 
called  tautomerism,  tautomeric  compounds  being  such  as  possess 
a  double  function  though  usually  represented  as  a  single  sub- 
stance. In  this  way  they  differ  from  the  usual  cases  of  isomerism 
in  which,  when  the  structure  is  once  determined  by  the  reactions 
of  formation,  the  arrangement  is  a  stable  one.  The  hydroxy  form 
is  known  as  the  enol  modification,  and  the  other  the  keto  form. 

Acetoacetic  ester  is  a  liquid  of  pleasant  strawberry-like  odor, 
which  boils  at  181°.  It  is  only  slightly  soluble  in  water,  and  is  col- 
ored violet  by  a  solution  of  ferric  chloride.  This  color  reaction  is 
common  to  compounds  having  an  unsaturated  alcohol  group,  and 
is  evidence  of  the  presence  of  some,  at  least,  of  the  ester  repre- 
sented by  the  first  formula.  Treated  with  cold,  dilute  alkali,the 
ester  is  saponified  into  the  alkali  salt  of  acetoacetic  acid  and  alco- 
hol. Heated  with  stronger  solutions  of  alkalies,  it  is  partly  con- 
certed into  alkali  acetate  and  alcohol: 


INTRODUCTION   TO    ORGANIC    CHEMISTRY  176 

CH3.CO.CH2.CO.OC2H5  +  2KOH  =  2CH3.CO.OK  +  C2H5OH 

and  partly  hydrolyzed  into  acetone,  alcohol  and  carbon  dioxide: 
CH3.CO.CH2.CO.OC2H5+H2O  =  CH3.CO.CH3+C2H5OH+CO2. 

This  latter  reaction  occurs  completely  when  it  is  heated  with 
dilute  acids.  There  are,  therefore,  two  distinct  varieties  of  hy- 
drolysis possible  which  may  be  distinguished  as  ketone  hydrolysis 
and  acid  hydrolysis. 

The  most  notable  property  of  acetoacetic  ester  is  that  of 
forming  compounds  with  metals,  which  are  either  of  the  type, 
CH3.CONa:CH.CO.OC2H5,  or  CH3.CO.CHNa.CO.OC2H5. 

By  treating  the  sodium  compound  with  alkyl  halides,  alkyl 
groups  are  introduced  in  place  of  the  metals,  and  since  the  sub- 
stituted esters  undergo  decompositions  of  the  same  character  as 
the  ester  itself,  many  substitution  derivatives  of  acetone  and 
acetic  acid  may  be  prepared  in  this  way. 

In  general  the  ester  shows  the  characteristic  ketone  reactions: 
By  nascent  hydrogen  it  is  converted  into  /3-hydroxybutyric  acid, 
CH3 .  CHOH .  CH2CO .  OH;  it  forms  a  crystalline  addition  product 
with  acid  sodium  sulphite,  etc.  Further,  acetyl  substitution 
products  are  not  formed  by  acetic  acid,  or  its  chloride  or  anhy- 
dride, substances  which  always  react  with  hydroxyl  groups. 

Reactions  of  acetoacetic  ester  that  are  characteristic  of  ketones 
are:  the  formation  of  /3-hydroxybutyric  acid  on  reduction;  the 
production  of  additive  compounds  with  hydrogen  cyanide  and 
with  acid  sodium  sulphite;  and  the  hydrolysis  of  the  ester  and  of 
its  alkyl  derivatives  by  alkalies  and  acids  into  acetone  and  its 
homologues.  Further,  with  acetic  anhydride  the  ester  yields  so 
little  of  an  acetyl  derivative  that  the  presence  of  an  hydroxyl 
group  seems  very  improbable,  and  acetyl  chloride  acting  on  the 
sodium  compound  gives  mainly  diacetoacetic  ester: 

CH3.CO.CHNa.CO.OC2H5  +  CH3.CO.C1  = 

(CH3.CO)2CH.CO.OC2H5  +  NaCl 


Ij6a          DERIVATIVES    OF    POLYHYDROXYL    ALCOHOLS 

On  the  other  hand,  the  acidic  character  of  the  ester  indicates  the 
hydroxyl  form,  and  ammonia  and  amines  yield  amino  and  alkyl- 
amino  crotonic  esters  of  the  general  formula:  CH3.C(NR2):- 
CH.CO.OC2H5. 

It  is  now  generally  agreed  that  the  free  acetoacetic  ester  con- 
sists chiefly  of  the  ketonic  form,  while  the  solid  sodium  compound 
must  be  represented  by  the  isomeric  formula  as  a  derivative  of 
0-hydroxycrotonic  acid. 


CHAPTER  XIV 

POLYBASIC  ACIDS  AND  ALCOHOL-ACIDS 
SOME  DIBASIC  ACIDS 

Name  Formula  Melting  Point 

Oxalic  CO.OH.CO.OH  189°  -(Anhydrous) 

Malonic  CO.OH.CH2.CO.OH  132 

Succinic  CO.OH.(CH2)2.CO.OH  184 

Glutaric  CO.OH.(CH2)3.CO.OH  98 

Adipic  CO.OH.(CH2)4.CO.OH  153 

Pimelic  CO.OH.(CH2)5.CO.OH  105.5 

Suberic  CO.OH.(CH2)6.CO.OH  141 

Azelaic  CO.OH.(CH2)7.CO.OH  108 

Sebacic  CO.OH.(CH2)8.CO.OH  134.5 

Oxalic  acid,  (CO.OH)2,  one  of  the  well-known  organic  acids,  is 
one  of  the  products  formed  when  ethyl  alcohol  or  glycol  is  oxidized 
by  nitric  acid,  and  also  results  from  the  oxidation  of  many  more 
complex  organic  substances.  When  sugar,  for  instance,  is  warmed 
with  concentrated  nitric  acid,  a  strong  reaction  occurs,  and  oxalic 
acid  crystallizes  from  the  resulting  solution  as  it  cools.  It  is 
prepared  commercially  from  saw-dust  by  mixing  it  with  a  strong 
solutionof  potassium  hydroxide  and  heating  to  about  250°;  or,  more 
usually  now,  by  heating  an  alkali  formate  (see  p.  106,  and  below). 
The  potassium  oxalate  produced  is  extracted  with  water,  changed 
into  the  insoluble  calcium  oxalate  by  milk  of  lime,  and  the  acid 
set  free  by  sulphuric  acid.  The  white  crystalline  solid  which  is 
obtained  from  solutions  of  oxalic  acid  contains  two  molecules  of 
water  of  crystallization.  It  begins  to  lose  water  at  30°  and 
becomes  anhydrous  at  100°.  On  further  careful  heating,  the  an- 
hydrous acid  sublimes,  and  this  fact  is  employed  for  its  purifica- 
tion, as  it  is  thus  readily  freed  from  the  small  amount  of  its  salts 
which  crystallize  with  it  The  acid  is  moderately  soluble  in  water, 

177 


178  INTRODUCTION  TO    ORGANIC  CHEMISTRY 

more  readily  soluble  in  alcohol,  and  nearly  insoluble  in  ether. 
When  strongly  heated,  it  breaks  down  into  carbon  dioxide,  carbon 
monoxide,  and  water,  with  the  production  of  some  formic  acid  as 
an  intermediate  step: 

CO.OH 

=  HCO.OH  +  CO2=  CO2  -f  CO  +  H2O 
CO.OH 

Heated  with  concentrated  sulphuric  acid,  it  gives  the  end  products 
of  water  and  the  oxides  of  carbon  at  once. 

The  relation  of  oxalic  acid  to  formic  acid  is  of  interest.  As 
stated,  some  formic  acid  is  produced  when  oxalic  acid  is  heated, 
and  the  usual  method  for  the  preparation  of  formic  acid  is  by 
heating  oxalic  acid  with  glycerol  (p.  104);  on  the  other  hand, 
when  an  alkali  formate  is  sharply  heated  (400°)  with  exclusion  of 
air,  the  alkali  oxalate  is  produced: 

HCO.OK   CO.OK 

=  |      +  H2 
HCO.OK   CO.OK 

From  two  molecules  of  formate  one  molecule  of  oxalate  is  formed, 
with  hydrogen  as  a  by-product;  and  one  molecule  of  oxalic  acid 
yields  one  molecule  of  formic  acid  with  carbon  dioxide  as  a  by- 
product; the  two  by-products  being  equivalent  to  the  one  mole- 
cule of  formic  acid  which  is  lost  in  completing  the  cycle. 

Besides  this  formation  of  oxalic  acid  from  formic  acid,  two  other 
methods  of  theoretical  interest  may  be  given:  An  alkali  oxalate  is 
obtained  when  carbon  dioxide  is  led  over  sodium  or  potassium 
heated  to  360°: 

2Na  +  2CO2  =  (CO.ONa)2 

By  hydrolysis  of  cyanogen,  the  acid  or  its  salts  are  formed,  cyan- 
ogen thus  showing  itself  to  be  the  nitrile  of  oxalic  acid: 

CN  CO.NH2  CO.ONH4 

|      +  2H20  =  |  +  2H20  =  | 

CN  CO.NH2  CO.ONH4 


POLYBASIC   ACIDS   AND   ALCOHOL-ACIDS  179 

Oxalic  acid  resists  the  oxidizing  action  of  nitric  acid,  as  is  evi- 
dent from  its  preparation  by  means  of  this  acid;  but  it  is  readily 
oxidized  in  sulphuric  acid  solutions  by  potassium  permanganate, 
and  is  used  in  volumetric  analysis  to  standardize  permanganate 
solutions.  The  reaction  is,  at  first,  slow,  but  soon  becomes  instan- 
taneous, being  accelerated  by  the  catalytic  effect  of  the  manganous 
sulphate  which  is  formed.  When  manganous  sulphate  is  added 
before  the  titration  begins,  the  permanganate  is  instantly  de- 
colorized. 

Salts  and  Esters  of  Oxalic  Acid. — Oxalic  acid  is  a  strong  dibasic 
acid,  being  highly  ionized  in  its  solutions.  Its  salts,  chiefly  the 
acid  potassium  oxalate  and  calcium  oxalate,  are  found  in  many 
plants,  such  as  sorrel  and  rhubarb,  and  crystals  of  calcium  oxalate 
are  found  generally  in  the  cell- walls  of  plants.  Ammonium  oxa- 
late is  a  well-known  laboratory  reagent. 

Besides  the  acid  and  normal  potassium  salts,  another  salt  called 
potassium  tetroxalate,  (CO.O)2HK.(CO.OH)2.2H2O,  is  readily 
obtained  pure.  It  is  sometimes  used  as  a  standard  substance  in 
volumetric  analysis  and  is  sold  as  "salt  of  sorrel"  for  removing 
rust  and  ink  stains  (of  iron  inks) .  The  insolubility  of  calcium  oxa- 
late in  acetic  acid  serves  as  a  test  for  calcium  and  for  oxalic  acid. 
Many  double  oxalates  are  known.  Potassium- ferrous  oxalate, 
K2Fe(C2O4)2,  made  by  mixing  solutions  of  ferrous  sulphate  and 
potassium  oxalate,  is  a  powerful  reducing  agent,  and  used  as  a 
developer  in  photography.  The  corresponding  ferric  salt,  K3Fe- 
(C2O4)s,  is  reduced  to  the  ferrous  compound  by  light,  and  this 
reaction  is  the  basis  for  making  platinum  prints.  The  paper 
coated  with  the  double  salt  is  exposed  under  a  negative  and  then 
treated  with  a  solution  of  platinum  salt.  The  platinum  is  reduced 
and  deposited  in  proportion  to  the  change  which  the  light  has 
produced.  Oxalic  acid  and  some  of  its  salts  are  used  as  mordants. 

Of  the  esters  of  oxalic  acid,  the  dimethyl  ester,  C2O4(CH3)2, 
is  used  for  preparing  pure  methyl  alcohol.  It  is  prepared  by 
dissolving  anhydrous  oxalic  acid  in  the  alcohol  and  heating. 


l8o  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

Methyl  oxalate  is  a  solid  which  melts  at  54°.  Ethyl  oxalate, 
made  in  a  similar  manner,  is  a  pleasant  smelling  liquid,  boiling 
at  186°. 

Other  Derivatives.— The  acid  chloride,  C1.CO.CO.C1,  cannot 
be  made.  Phosphorus  pentachloride  acts  as  a  dehydrating  agent 
in  this  case,  and  gives  carbon  dioxide,  carbon  monoxide,  phos- 
phorus oxychloride,  and  hydrogen  chloride. 

CO.NH2 

Oxalic  acid  amide  or  oxamide,  ,  is  formed  when  am- 

CO.NH2 

monium  oxalate  is  heated;  when  a  neutral  oxalic  ester  is  shaken 
with  aqueous  ammonia;  or  from  cyanogen  by  the  action  of  water 
in  the  presence  of  a  trace  of  aldehyde.  It  is  a  white  crystalline 
substance,  almost  insoluble  in  water,  alcohol  or  ether.  When 
heated  it  partly  sublimes  unchanged  and  partly  decomposes  into 
cyanogen  and  water.  When  heated  to  200°  with  water  it  is 
converted  into  ammonium  oxalate. 

When  acid  ammonium  oxalate  is  heated,  the  first  product  is 
oxamic  acid,  NH2.CO.CO.OH.  The  anhydride  of  oxalic  acid 
does  not  exist. 

Malonic  acid,  CO.OH.CH2.CO.OH,  may  be  looked  at  as 
acetic  acid  in  which  carboxyl  has  been  substituted  for  one  hydro- 
gen atom  in  the  CH3  group.  It  is,  in  fact,  made  from  acetic  acid 
by  such  substitution.  Monochloracetic  acid,  CH2C1.CO.OH,  is 
first  made,  and  after  conversion  into  the  potassium  salt,  is 
changed  into  the  cyanacetate,  CH2.CN.CO.OK,  by  means  of 
potassium  cyanide.  This  is  the  nitrile  of  malonic  acid,  and  from 
it  the  acid  (or  its  salt)  is  obtained  in  the  usual  way  by  hydrolysis. 
This  method  of  formation  is  satisfactory  evidence  of  the  consti- 
tution of  the  acid. 

Malonic  acid  was  first  observed  as  an  oxidation  product  of 
malic  acid  (p.  185),  and  its  name  was  given  it  on  account  of  this 
origin.  It  is  a  solid,  melting  at  I33°-I34°,  and  very  soluble  in 
water  and  in  alcohol. 


POLYBASIC  ACIDS   AND   ALCOHOL-ACIDS  l8l 

Heated  a  little  above  its  melting  point,  malonic  acid  breaks 
up  quantitatively  into  carbon  dioxide  and  acetic  acid: 

CO.  OH 

CH2        =  CHa.CO.OH-f  CO2 

I 
CO.OH 

This  is  a  typical  general  reaction  which  takes  place  on  heating 
compounds  containing  two  carboxyl  groups  united  to  the  same 
carbon  atom.  We  have  here  an  unstable  arrangement,  which  is 
like  that  already  noticed  in  the  case  of  hydroxyl  groups;  but 
while,  in  general,  the  dihydroxyl  combination  is  unstable  under 
all  conditions,  the  dicarboxyl  compounds  decompose  only  when 
heated  to  their  melting  point  or  above.  When  a  compound 
contains  two  carboxyl  groups  which  are  not  immediately  united 
to  the  same  carbon  atom,  it  decomposes  on  heating  with  the  loss 
of  the  elements  of  water  and  formation  of  an  anhydride.  Thus  in 
the  case  of  succinic  acid  (p.  184): 

CH2.CO.OH     CH2.CO\ 

|  =|  >0  -f  H20 

CH2.CO.OH      CH2.CCK 

Ethyl  malonate,  CH2(CO.OC2H5)2,  has  a  special  interest 
because  of  the  fact  that  one  or  both  of  the  hydrogen  atoms  of  the 
CH2  group  can  be  replaced  by  sodium.  The  ester  itself  may  be 
made  by  the  reaction  of  malonic  acid  with  alcohol,  but  is  usually 
prepared  by  treating  a  mixture  of  cyanacetate  of  potassium 
(made  as  above)  and  alcohol  with  hydrogen  chloride.  It  is  a 
liquid,  boiling  at  198°.  When  sodium  is  added  to  it,  hydrogen 
is  evolved  and  CHNa(CO.OC2H5)2  or  CNa2(CO.OC2H5)2  is 
formed  according  to  the  proportion  of  sodium  used.  These 
sodium  compounds  are  also  formed  by  the  action  of  sodium 
ethoxide  on  the  ester.  In  this  case  intermediate  addition  prod- 
ucts are  probably  formed  as  in  the  case  of  acetoacetic  ester 


1 82  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

(p.  174).  The  structure  of  the  resulting  sodium  compounds,  as 
in  that  case,  is  in  doubt.  Most  of  the  reactions,  however,  are  in 
agreement  with  the  formulas  given  above.  These  sodium  com- 
pounds react  readily  with  alkyl  halides  and  with  acetyl  chloride, 
giving  replacements  of  the  sodium  by  alkyl  groups  or  by  the  acetyl 
group.  By  hydrolysis  of  these  substituted  esters  the  substituted 
dibasic  acids  are  obtained;  and  from  these,  on  heating,  carbon 
dioxide  is  split  out  as  in  the  decomposition  of  malonic  acid  by 
heat  and  the  corresponding  substituted  monobasic  acid  is  made. 
For  instance,  the  sodium  compound,  CHNa(CO.OC2H5)2  with 
CO.OC2H5  CO.OH 

I  I 

C2H5I  gives  CH(C2H5)  ,  and  this  on  hydrolysis  yields  CH(C2H5), 

CO.OC2H5  CO.OH 

H 

which    on    heating  =  CH.(C2H5)    or     CH3.CH2.CH2.CO.OH, 

CO.OH 

ethyl  acetic  acid  or  normal  butyric  acid.  This  method  of  malonic 
acid  synthesis  is,  therefore,  a  very  useful  means  for  making  a  great 
variety  of  compounds,  and  is  especially  employed  for  the  synthesis 
of  isomonobasic  acids.  A  step-by-step  replacement  makes  it 
possible  to  substitute  two  different  alkyl  groups  for  the  two  hydro- 
gen atoms  in  the  CH2  group  of  malonic  acid. 

Other  Derivatives  of  Malonic  Acid 

Among  other  derivatives  the  hydroxyl  substitution  products 
have  the  most  interest. 

Tartronic  acid,  CO.OH.CHOH.CO.OH,  or  monohydroxy- 
malonic  acid,  can  be  made  by  the  usual  method  for  replacing 
hydrogen  by  hydroxyl :  formation  of  brommalonic  acid  by  direct 
action  of  bromine,  and  treatment  of  this  with  silver  hydroxide. 
The  name  of  this  acid  is  derived  from  tartaric  acid,  from  which 


POLYBASIC   ACIDS   AND   ALCOHOL-ACIDS  183 

it  was  first  prepared  by  oxidation.     It  is  a  solid,  melting  at  187°. 

Dihydroxymalonic  acid,  CO.OH.C(OH)2.CO.OH,  can  be 
made  from  dibrommalonic  acid  by  boiling  it  with  barium 
hydroxide.  Although  this  acid  can  be  melted  without  loss  of 
water,  and  forms  salts  which  correspond  to  the  formula  given  for 
the  acid,  it  deports  itself  in  reactions  like  a  ketone-acid,  mesoxalic 
acid,  CO  .OH. CO. CO. OH.  Esters  of  both  forms  are  known. 

Dihydroxymalonic  acid  is  interesting  as  one  of  the  very  small 
number  of  compounds  which  appear  to  contain  two  hydroxyl 
groups  united  to  a  single  carbon  atom  (cf.  p.  113).  It  is  evident, 
however,  from  the  ketone  reactions  it  gives,  that  the  combination 
is  rather  unstable. 

The  acid  melts  at  115°,  and  at  higher  temperatures  decomposes 
into  carbon  dioxide,  water,  and  glyoxylic  acid: 

CO.OH.C(OH)2.CO.OH  =  CHO.CO.OH  +  CO2  +  H26 

and  on  evaporation  of  its  aqueous  solution  it  breaks  up  into  carbon 
monoxide,  oxalic  acid,  and  water: 

CO.OH.C(OH)2.CO.OH  =  (CO.OH)2  +  CO  +  H2O 

The  appearance  of  carbon  monoxide  in  this  reaction  causes  it  to 
reduce  ammoniacal  silver  nitrate  with  evolution  of  carbon  dioxide. 
By  sodium  amalgam  it  is  reduced  to  tartronic  acid,  and  it  unites 
with  acid  sodium  sulphite  like  a  ketone. 

Succinic  acid,  CO.OH.CH2.CH2.CO.OH,  occurs  in  many  plants, 
in  fossil  wood,  and  derives  its  name  from  the  fact  that  it  is  a  prod- 
uct of  the  distillation  of  amber  (succinum).  It  is  prepared  for 
medicinal  purposes  from  amber,  but  may  also  be  made  by  the 
fermentation  of  calcium  malate  or  ammonium  tartrate;  or  syn- 
thetically from  propionic  acid,  or  from  ethylene  by  the  usual 
method  of  forming  the  corresponding  cyanogen  compounds 
(nitriles).  It  is  produced  in  small  amounts  in  the  alcoholic  fer- 
mentation of  sugar,  and  is  frequently  one  of  the  products  of  the 
oxidation  of  fatty  acids,  etc.,  of  higher  molecular  weight,  by  nitric 


184  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

acid.     The  structure  of  succinic  acid  is  clear  from  the  methods  of 
its  synthetic  formation. 

It  melts  at  182°,  and  boils  at  235°,  decomposing  in  great 
part  into  its  anhydride.  Dehydrating  agents  also  produce  the 
anhydride, 

CH2.C< 


CH2.C( 

CH2.CO.NH2 

Succinamide. — The  amide  of  succinic  acid,   |  ,  can 

CH2.CO.NH2 

be  prepared,  like  other  acid  amides,  by  the  reaction  of  an  ester  of 
succinic  acid  with  ammonia.  It  behaves,  in  general,  like  other  acid 
amides,  but  when  strongly  heated  does  not  give  the  corresponding 

CH2.CN 
nitrile,    |  ,  with  loss  of  the  elements  of  water,  but  loses  one 

CH2.CN 
molecule  of  ammonia  with  conversion  into  a  compound  whose 

CH2.C  =  O 
structure  appears  to  be,  I         ^r^NH,  succinimide  (NH  being 

CH2.C  =  0 

the  imido  group).  This  compound  is  also  formed  by  distilling 
ammonium  succinate,  and  by  heating  succinic  anhydride  in  a 
current  of  ammonia. 

Succinic  anhydride  and  the  imide  both  have  formulas  in  which 
there  is  a  closed  ring  of  atoms  instead  of  the  open  single  or 
branched  chains  which  represent  the  structure  of  most  of  the  ali- 
phatic compounds.  The  tendency  to  form  such  closed  rings,  or 
cyclic  compounds,  is  most  pronounced  where  the  ring  contains 
five  or  six  connected  atoms;  others  with  a  smaller  or  larger  num- 
ber are  formed,  but  are  less  stable  (cf.  p.  257). 

Succinamide  melts  at  242-243°  and  is  somewhat  soluble  in 
water.  Succinimide  melts  at  1 26°,  boils  at  287-288°  and  is  readily 
soluble  in  water.  Its  reaction  is  neutral,  but  the  hydrogen  of  the 
imido  group  is  replaced  by  metals  more  readily  than  that  of  the 
amido  group  in  acid  amides. 


POLYBASIC   ACIDS   AND   ALCOHOL-ACIDS  185 

Isosuccinic  acid,  CH3.CH(CO.OH)2,  is  a  methyl  derivative  of 
malonic  acid,  and  decomposes  like  this,  when  heated,  giving  pro- 
pionic  acid  and  carbon  dioxide: 

CH3.CH(CO.OH)2  =  CH3.CH2.CO.OH  +  CO2 

Hydroxyl  Derivatives  of  Succinic  Acid 

CH.OH.CO.OH 

Malic  acid,    |  ,  is   monohydroxy-succinic   acid. 

CH2.CO.OH 

It  was  first  obtained  from  unripe  apples  (malum)  and  owes  its 
name  to  that  fact.  It  occurs  very  generally  in  acid  fruits,  such  as 
gooseberries  and  currants,  and  is  found  in  the  roots,  leaves  and 
seeds  of  many  plants  and  vegetables.  It  is  readily  prepared  from 
the  berries  of  the  mountain  ash.  The  juice  of  the  berries  is 
neutralized  with  calcium  hydroxide,  and  the  acid  obtained  from 
the  difficultly  soluble  calcium  salts  by  means  of  sulphuric  acid. 
Another  good  source  of  malic  acid  is  the  so-called  "maple  sugar 
sand"  formed  in  the  making  of  maple  sugar.  The  acid  may  also 
be  made  by  the  usual  synthetic  methods.  It  melts  at  100°,  and 
at  a  somewhat  higher  temperature  begins  to  decompose.  Instead 
of  forming  an  anhydride  by  loss  of  water  from  the  carboxyl 
groups,  however,  the  decomposition  is  similar  to  that  of  the  /?- 
hydroxy-monocarboxylic  acids  with  the  production  of  an  un- 
saturated  acid  (p.  172).  At  I4o°-i5o°  the  chief  product  is 
fumaric  acid.  When  heated  rapidly  to  180°,  male'ic  anhydride 
is  a  considerable  product  which  is  readily  converted  into  maleic 
acid  by  water. 

The  malic  acid  obtained  from  fruits  is  optically  active,  but  its 
solutions  show  a  somewhat  unusual  behavior  in  that  the  rotatory 
power  changes  with  their  concentration,  so  that  dilute  solutions 
are  levo-rotatory,  while  concentrated  solutions  are  dextro-rota- 
tory. From  the  synthetic  malic  acid,  which  is  inactive,  two  oppo- 
sitely active  acids  can  be  obtained  by  means  of  the  cinchonine 


1 86  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

salts.  It  will  be  noticed  that  the  formula  of  the  acid  contains  an 
asymmetric  carbon  atom. 

Fumaric  and  maleic  acids,  which  are  formed  by  heating  malic  acid 
and  can  be  made  in  other  ways,  present  an  interesting  case  of  phy- 
sical isomerism.  The  simple  formula  which  stands  for  either  is 
CH.CO.OH 

||  .     There  is  no  asymmetric  carbon  atom  and  no  op- 

CH.CO.OH 

tical  activity,  but  the  two  acids  differ  widely  in  their  solubility, 
their  crystalline  form,  and  their  behavior  when  heated.  Fumaric 
acid  which  occurs  in  many  plants,  in  Iceland  moss,  and  in  some 
fungi,  is  the  more  stable  of  the  two  isomers.  It  is  very  sparingly 
soluble,  and  volatilizes  at  200°,  without  melting.  When  heated 
higher  it  decomposes  into  water  and  maleic  anhydride, 
CH.COv 

yO  with  partial  charring.     Maleic  acid  is  exceedingly 
CH.CCX 

soluble,  melts  at  130°,  and  at  160°  boils  and  decomposes  into  water 
and  its  anhydride.  It  is  converted  into  fumaric  acid  when  heated 
with  water  at  130°,  and  under  several  other  conditions.  Maleic 
acid  solutions  are  precipitated  by  barium  hydroxide,  fumaric 
acid  solutions  are  not.  Other  instances  of  similar  isomeric  pairs 
are  known  among  unsaturated  compounds. 

Stereo-isomerism  of  Unsaturated  Compounds. — Fumaric  and 
maleic  acids  present  a  case  of  isomerism  like  that  of  crotonic  and 
isocro tonic  acids  (p.  in),  in  which  decided  differences  in  physical 
behavior  are  to  be  accounted  for.  An  explanation  given  by 
stereochemistry  is,  in  brief,  as  follows: 

When  a  compound  contains  two  carbon  atoms  united  by  a 
single  bond,  the  tetrahedral  formula  is  that  shown  in  i.  When 
each  of  the  carbon  atoms  is  joined  to  four  different  atoms  or 
groups  (is  asymmetrical),  we  may  have  such  optical  isomerism 
as  is  shown  by  lactic  or  tartaric  acid  (pp.  165  and  193).  But 
in  any  other  case  the  free  rotation  possible  to  the  carbon  atoms 
about  their  common  axis  is  unattended  by  isomerism  of  any  kind 


POLYBASIC   ACIDS   AND   ALCOHOL-ACIDS 


I87 


except  that  provided  for  by  the  usual  structural  formulas.  If, 
however,  the  carbon  atoms  are  united  by  a  double  bond,  it  is  as- 
sumed that  their  rotation  is  no  longer  possible,  and  the  condition 
is  represented  by  2,  where  the  two  tetrahedra  are  shown  with  one 


H 


[.  Ethane 


2.  Ethylene 


edge  in  common,  indicating  the  double  bond.  Diagram  i  is 
the  stereochemical  formula  of  ethane,  2  that  of  ethylene.  If 
two  different  atoms  or  groups  are  united  to  each  of  the  carbon 


CO.OH 


CO.OH, 


CO.OH 


CO.OH 


3.  Maleic  acid 


4.  Pumaric  acid 


atoms  joined  by  a  double  bond,  two  distinct  arrangements  can 
be  made,  as  shown  in  3  and  4,  which  give  the  stereochemical 


1 88 


INTRODUCTION   TO    ORGANIC   CHEMISTRY 


formulas  of  male'ic  and  fumaric  acids.  In  these  diagrams,  as 
in  those  for  the  lactic  acids  and  tartaric  acids,  the  two  forms 
cannot  be  superposed,  but,  unlike  the  cases  of  optical  isomers, 
one  is  not  the  mirror  image  of  the  other.  This  type  of  isomer- 
ism  which  is  shown  by  fumaric  and  maleic  acids,  and  by  cro- 
tonic  and  isocrotonic  acids,  as  well  as  by  other  unsaturated 
compounds,  is  called  geometric  isomerism,  since  the  four  atoms 
or  groups  united  to  the  carbon  atoms  are  represented  as  ly- 
ing in  the  same  plane.  The  two  configurations  may  also  be 
shown  in  diagrams  which  present  the  tetrahedral  axes,  as  follows: 


CO.OH 


CO.OH 


CO.OH 


CO.OH 


5.  Fumaric  acid 


6.  Maleic  acid 


The  corresponding  projection  formulas  which  are  commonly  used 
for  these  representations  are: 


H—C— CO.OH 

II 
H—C— CO.OH 

Maleic  acid 

CO.OH— C—H 

II 
CH3— C— H 

Isocrotonic  acid 


CO.OH— C—H 

II 
H—C— CO.OH 

Fumaric  acid 

CO.OH— C—H 

II 
H— C— CH3 

Crotonic  acid 


POLYBASIC   ACIDS   AND   ALCOHOL-ACIDS  1 89 

The  assignment  of  the  formulas  to  the  maleic  and  fumaric  acids, 
as  above,  is  based  on  the  assumption  that  the  positions  of  the 
carboxyl  groups  in  the  maleic  acid  formula  is  the  more  favorable 
one  for  the  formation  of  the  anhydride  which  maleic  acid  forms 
more  readily  than  fumaric  acid.  This  arrangement  with  like 
groups  on  the  same  side  is  called  the  cis  or  malemoid  form,  and 
the  other,  with  opposed  positions,  the  trans  or  fumaroid  form. 
The  latter  is  always  given  to  the  more  stable  isomer,  as  in  the  case 
of  the  cro tonic  acids  (p.  in). 

Tartaric  acid,  CO.OH.CHOH.CHOH.CO.OH,  is  dihydroxy- 
succinic  acid.  This  well-known  acid  is  widely  distributed  in  na- 
ture both  as  free  acid  and  in  the  form  of  potassium  and  calcium 
salts.  Acid  potassium  tartrate,  especially,  is  found  in  many  fruits, 
and  is  present  in  considerable  amount  in  the  juice  of  grapes.  As 
this  salt  is  even  less  soluble  in  alcohol  than  in  water,  it  is  pre- 
cipitated in  wine  casks  as  alcohol  is  formed  by  the  fermentation 
of  the  grape-juice.  Tannin  and  other  substances  are  deposited 
with  it,  forming  crystalline  crusts  which  are  known  as  argol,  and 
from  this  the  pure  acid  tartrate  and  the  acid  are  prepared. 

Preparation. — To  obtain  the  pure  salt,  the  crude  argol  is  boiled 
with  water  and  bone  black,  the  solution  filtered,  and  then  evapo- 
rated to  crystallization.  For  the  preparation  of  the  acid,  the 
nearly  insoluble  calcium  tartrate  is  precipitated  from  a  solution 
of  argol  by  chalk  (or  gypsum),  and  after  filtration  the  acid  is 
set  free  by  sulphuric  acid  (with  precipitation  of  calcium  sul- 
phate), and  the  tartaric  acid  is  then  crystallized  from  the  clear 
solution. 

Uses. — Tartaric  acid  and  the  acid  potassium  salt  are  used  in 
medicine,  in  dyeing  and  calico  printing,  and  for  other  purposes. 
Under  the  name  of  "cream  of  tartar"  acid  potassium  tartrate  is 
largely  used  as  an  ingredient  of  one  class  of  baking  powders. 
Potassium  sodium  tartrate,  known  as  "Rochelle  salt,"  has  long 
been  used  in  medicine,  especially  in  Seidlitz  powders  which  con- 
tain (i)  this  salt  with  sodium  bicarbonate  and  (2)  tartaric  acid. 


I QO  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

In  the  laboratory  it  is  used  in  the  preparation  of  Fehling's  solution. 
Tartar  emetic,  potassium  antimonyl  tartrate,  CO.OK.CHOH. 
CHOH.CO.O(SbO),  is  used  as  a  mordant,  and  was  formerly 
considered  an  important  remedy. 

Properties. — Tartaric  acid  crystallizes  in  long  monoclinic 
prisms.  It  melts  at  i68°-i7o°,  and  when  heated  somewhat 
above  its  melting  point,  loses  the  elements  of  water  with  the 
formation  of  several  substances  which  may  be  considered  as 
anhydrides,  since  they  are  converted  into  tartaric  acid  again  by 
boiling  with  water.  At  higher  temperatures  a  more  profound 
decomposition  occurs;  the  acid  becomes  brown  and  chars,  giving 
an  odor  like  burnt  sugar,  and  a  distillate  may  be  obtained  which 
contains  pyrotartaric  (methyl  succinic)  and  pyroracemic  (p.  173) 
acids.  When  heated  with  concentrated  sulphuric  acid,  tartaric 
acid  chars,  and  carbon  monoxide,  dioxide,  and  sulphur  dioxide  are 
evolved.  Tartaric  acid  is  readily  soluble  in  water  and  in  alcohol, 
but  insoluble  in  ether.  When  its  solution  is  boiled  alone  or  with 
addition  of  hydrochloric  acid,  tartaric  acid  is  partly  converted 
into  the  isomeric  racemic  acid.  Tartaric  acid  is  readily  oxidized 
in  solution.  Ammoniacal  silver  nitrate  solutions  are  reduced 
by  it,  and  it  is  used  in  making  silver  mirrors.  Solutions  of  the 
acid  and  of  its  salts  are  subject  to  change  through  the  action  of 
moulds  and  bacteria,  and  consequently  do  not  keep  well  when 
exposed  to  the  air.  Succinic  acid  may  be  prepared  from  am- 
monium tartrate  by  bacterial  fermentation.  Calcium  tartrate, 
on  the  other  hand,  yields  no  succinic  acid,  but  gives  volatile 
fatty  acids,  acetic,  propionic,  and  butyric.  Solutions  of  tartaric 
acid  and  its  salts  are  optically  active,  being  dextro-rotatory. 

Tartaric  acid  is  readily  proved  to  be  a  dibasic  acid,  and  its 
constitutional  formula,  which  represents  it  as  dihydroxy  succinic 
acid,  is  established  by  its  reduction  (by  HI)  to  malic  and  then  to 
succinic  acid.  Other  evidence  to  the  formula  is  found  in  the 
synthesis  of  racemic  acid  whose  relation  to  tartaric  acid  will  now 
be  discussed. 


POLYBASIC   ACIDS   AND   ALCOHOL-ACIDS  IQI 

Racemic  acid  is  an  acid  of  the  same  composition  as  tartaric 
acid,  but  which  differs  from  the  latter  in  several  particulars.  It 
crystallizes  in  a  different  form  (triclinic)  and  with  one  molecule  of 
water  of  crystallization  which  is  lost  at  110°,  and  the  acid  melts 
with  decomposition  at  205-206°.  It  is  much  less  soluble  in  water 
than  tartaric  acid,  and  the  solutions  are  optically  inactive.  Its 
salts,  the  racemates,  often  differ  from  the  tartrates  of  the  same 
metals  both  in  their  crystalline  form  and  in  their  water  of  crystal- 
lization and  solubility.  The  calcium  racemate  is  still  less  soluble 
in  water  than  the  calcium  tartrate,  while  the  acid  potassium 
racemate  is  more  soluble.  These  differences  led  to  its  recognition 
and  separation  in  the  preparation  of  tartaric  acid  from  argol. 
Racemic  acid  is  formed  in  tartaric  acid  solutions  under  certain 
conditions,  and  this  probably  accounts  for  its  appearance  as  a 
by-product  in  the  working  up  of  argol,  though  it  or  its  salts  may 
be  a  natural  product.  Berzelius  proved  the  identity  of  its  com- 
position with  that  of  tartaric  acid  in  1830,  and  it  is  of  interest  to 
note  that  this  fact  together  with  the  earlier  discovery,  that  the 
fulminate  and  cyanate  of  silver  had  the  same  composition  (Liebig, 
1823),  and  some  other  similiar  instances,  led  to  the  introduction 
of  the  word  and  idea  of  isomerism  into  chemistry. 

Formation.' — Racemic  acid  is  formed  from  tartaric  acid  by 
boiling  it  for  some  time  with  water  or  with  solutions  of  hydro- 
chloric acid  or  sodium  hydroxide.  The  conversion  is,  however, 
under  these  conditions,  only  partial;  but  when  tartaric  acid  is 
heated  with  about  one-ninth  its  weight  of  water  to  125°  (in  a 
sealed  tube)  for  some  30  hours,  the  change  is  almost  complete. 
Racemic  acid,  together  with  mesotartaric  acid,  can  be  made  from 
dibromsuccinic  acid  by  substitution  of  hydroxyl  for  bromine: 

CO.OH.CHBr.CHBr.CO.OH  +  2AgOH 

=  CO.OH.CHOH.CHOH.CO.OH  +  2AgBr 

This  reaction,  which  gives  evidence  for  the  structural  formula  of 


IQ2  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

racemic  acid,  may  be  made  the  final  step  for  its  synthesis  from  the 
elements,  as  follows: 

2C  +  sH2  -*  CH2  :CH2  -»  CN.CH2CH2CN  -> 

CO.OH.CH2.CH2.CO.OH,  etc. 

Resolution  of  Racemic  Acid  into  Optically  Active  Tartaric 
Acids. — In  1848,  Pasteur  found  that  the  sodium  ammonium  salt 
of  racemic  acid  gave  two  sets  of  crystals  differing  slightly  in  the 
disposition  of  their  faces,  and  in  such  a  way  that  one  form  corre- 
sponded to  the  mirror  image  of  the  other.  On  separating  the  two 
kinds,  he  found  that  the  solution  of  one  kind  turned  the  plane  of 
polarized  light  to  the  right,  while  that  of  the  other  was  levo- 
rotatory.  When  the  acids  were  set  free  from  these  salts,  one 
proved  to  be  the  ordinary  dextro-rotatory  tartaric  acid,  and  the 
other  an  isomeric,  levo-rotatory  acid.  On  mixing  solutions  con- 
taining equal  weights  of  the  two  acids,  and  crystallizing,  racemic 
acid  is  obtained.  Pasteur  also  resolved  racemic  acid  into  the 
two  active  tartaric  acids  by  taking  advantage  of  the  different 
solubilities  of  compounds  which  the  two  acids,  mixed  in  racemic 
acid,  form  with  certain  optically  active  bases,  such  as  cinchonine. 
By  a  third  method,  consisting  in  the  action  of  certain  organisms, 
one  modification  may  be  destroyed,  leaving  the  other.  Thus 
penicillium  glaucum  in  a  solution  of  ammonium  racemate  causes 
the  dextro-tartrate  to  disappear,  and  ammonium  levo-tartrate  re- 
mains alone  in  solution. 

Racemic  acid,  like  ordinary  lactic  acid,  is,  therefore,  a  com- 
bination of  two  optically  active  isomeric  acids  whose  power  on 
polarized  light  is  equal,  but  opposite. 

The  work  of  Pasteur  by  which  these  facts  were  brought  out  is  of 
great  historical  interest,  as  it  gave  the  first  explanation  of  the 
relation  of  tartaric  and  racemic  acids,  and  was  the  first  time  that 
an  inactive  substance  was  resolved  into  optically  active  com- 
pounds. *  Racemic  is  now  used  as  a  general  term  to  designate  an 

1  See  Pasteur's  "  Researches  on  The  Molecular  Asymmetry  of  Natural 
Organic  Products,"  in  Alembic  Club  Reprints,  No.  14. 


POLYBASIC   ACIDS   AND   ALCOHOL-ACIDS  1 93 

inactive  substance  which  consists  of  a  mixture  of  dextro  and 
levo  forms. 

Mesotartaric  acid,  also  has  the  same  composition  as  tartaric 
acid,  and  is  formed  together  with  racemic  acid  when  ordinary 
tartaric  acid  is  heated  with  water  or  sodium  hydroxide;  but  its 
formation  takes  place  more  slowly  than  that  of  racemic  acid,  so 
that  the  yield  is  increased  by  prolonging  the  heating.  It  is  also 
formed  with  racemic  acid  by  the  synthesis  from  dibromsuccinic 
acid.  It  is  separated  from  ordinary  tartaric  and  racemic  acids 
by  taking  advantage  of  the  much  greater  solubility  of  its  acid 
potassium  salt.  'It  crystallizes  with  one  molecule  of  water  of 
crystallization  in  a  form  differing  from  those  of  the  other  acids, 
and  the  anhydrous  acid  melts  at  140°.  Its  solubility  is  about  the 
same  as  that  of  tartaric  acid,  but  its  solutions  are  optically  inac- 
tive, and  it  is  not  possible  to  resolve  the  acid  into  active  com- 
ponents. It  can,  however,  be  partly  converted  into  racemic  acid 
by  heating,  and  thus  indirectly  into  the  active  tartaric  acids.  Its 
structural  formula  is  the  same  as  that  of  racemic  acid  and  tartaric 
acid,  as  is  shown  by  its  formation  from  dibromsuccinic  acid. 

We  have,  therefore,/0w  dihydroxysuccinic  acids:  two  of  these 
are  optically  active,  turning  the  plane  of  polarized  light  to  an  equal 
degree  in  opposite  directions,  and  differing  in  no  other  respect 
except  in  the  modifications  of  their  crystalline  forms,  in  the 
solubility  of  the  compounds  they  form  with  optically  active 
organic  bases,  and  in  their  behavior  toward  certain  organisms. 
The  other  two  inactive  acids  differ  from  the  active  acids  and  from 
each  other  in  crystalline  form,  in  their  melting  points,  the 
solubility  of  their  salts,  etc.,  as  well  as  by  the  fact  that  one  of  them 
can  be  resolved  into  active  components,  while  the  other  cannot. 

Stereochemistry  of  the  Tartaric  Acids. — The  student  has 
noticed  that  the  structural  formula  for  these  acids  contains  two 
asymmetric  carbon  atoms.  One  such  atom  accounts  for  the 
existence  of  two  oppositely  active  and  one  inactive  compound,  as 
we  have  seen  in  a  former  discussion  (p.  169).  When  there  are 


194 


INTRODUCTION   TO   ORGANIC   CHEMISTRY 


two  or  more  asymmetric  carbon  atoms  in  the  molecule  the  prin- 
ciples of  stereochemistry  admit  the  possibility  of  a  larger  number 
of  physical  isomers.  With  two  as  in  this  case,  and  two  which  are 
each  combined  with  the  same  groups,  there  is  but  one  additional 
arrangement.  The  formulas  for  the  tartaric  acids  are: 


OH 


HO 


CO.OH 

i.  d-Tartaric  acid. 


OH 


HO. 


OH 


CO.OH 

3.  Mesotartaric  acid. 

CO.OH  CO.OH 

H--C— OH       HO— C— H 

I 
H— C— OH 

CO.OH 

2 


CO.OH 

4.  Mesotartaric  acid. 

HO.OC 


HO— C— H 


CO.OH 

i 


H-C— OH 

H— C— OH 

I 
CO.OH 

3 


CO.OH 
HO— C— H 
HO— C— H 

CO.OH 

4 


POL YB ASIC   ACIDS   AND   ALCOHOL-ACIDS  1 95 

The  lower  and  upper  halves  of  formula  i  or  2  can  be  exactly 
superposed,  and  we  may  suppose  that  each  half  therefore  sup- 
plements the  optical  activity  of  the  other.  One  molecule  will 
then  be  wholly  dextro-rotatory,  the  other  wholly  levo-rotatory. 
A  mixture  of  the  two  in  equal  amounts  will  be  inactive  through 
external  or  intermolecular  compensation.  This  accounts  for  the 
two  active  tartaric  acids  and  for  racemic  acid.  But  in  the  arrange- 
ments 3  or  4  the  lower  and  upper  halves  of  the  figure  cannot  be 
superposed;  one  half  of  each  formula  is  identical  with  one  of  the 
two  halves  of  i,  and  the  other  with  one  of  the  two  halves  of  2, 
so  that  both  levo  and  dextro  arrangements  are  present  in  the  same 
molecule,  and  there  is,  therefore,  optical  inactivity  through  in- 
ternal or  intramolecular  compensation.  This  is  the  representation 
of  mesotartaric  acid.  Formula  4  differs  in  no  essential  feature 
from  formula  3. 

CO.OH 

I 
Citric  acid,  CO.OH.CH2.C.CH2.CO.OH,  occurs  in  many  acid 

OH 

fruits  often  together  with  malic  and  tartaric  acids.  The  juice 
of  unripe  lemons  contains  6-7  per  cent,  of  citric  acid,  and  the  acid 
is  prepared  commercially  from  this  source.  It  is  first  precipitated 
as  the  calcium  salt  from  the  hot  clarified  juice  by  adding  powdered 
chalk  until  no  more  carbon  dioxide  is  evolved,  and  then  milk  of 
lime.  The  calcium  citrate,  after  thorough  washing  with  hot 
water,  is  decomposed  by  the  calculated  amount  of  sulphuric  acid 
which  precipitates  the  calcium  as  calcium  sulphate.  The  acid  is 
finally  purified  by  recrystallization.  It  is  readily  soluble  in 
water  and  in  alcohol.  It  ordinarily  crystallizes  with  one  mole- 
cule of  water,  which  is  lost  at  about  130.°  The  anhydrous  acid 
melts  at  153°,  and  recrystallizes  from  cold  water  without  water 
of  crystallization.  When  the  solid  acid  is  heated,  it  chars  and 
gives  irritating  vapors,  but  no  'odor  of  burnt  sugar  as  in  the  case 


ig6 


INTRODUCTION   TO   ORGANIC  CHEMISTRY 


of  tartaric  acid.  It  differs  from  tartaric  acid  also  by  charring 
much  less  readily  when  heated  with  concentrated  sulphuric  acid, 
and  by  the  fact  that  its  calcium  salt  is  more  soluble  in  cold  than 
in  hot  water.  Like  tartaric  acid  and  some  other  organic  acids, 
it  prevents  the  precipitation  of  certain  hydroxides  of  metals 
from  solutions  of  their  salts. 

The  acid  is  used  for  making  lemonade,  and  is  employed  in 
medicine  and  in  dyeing  and  calico  printing.  Magnesium  citrate, 
(CeHsOT^Mgs^HjjO,  is  a  readily  soluble  salt  which  is  used  in 
medicine  and,  mixed  with  acid  sodium  carbonate  and  sugar, 
forms  the  well-known  "effervescing  citrate  of  magnesia"  or 
"  fruit  salts.'7  Ferric  ammonium  citrate  is  used  in  making  "  blue- 
, print"  paper. 

Structure  of  Citric  Acid. — The  acid  is  readily  proved  to  be  a 
tribasic  acid  and  to  contain  one  hydroxyl  group  by  the  usual 
methods.  The  positions  of  the  hydroxyl  and  carboxyl  groups  is 
demonstrated  by  the  synthesis  of  the  acid  from  symmetrical 
dichloracetone  by  the  following  steps: 


CH2C1 


CH2C1         CH2C1 


CH2.CN          CH2.CO.OH 


HCN 

:o       ->( 

<OHnoH 
->< 
CN 

/OHxcN 

or        ->( 
XJO.OH 

/OH      HOH 

:<        ->( 

XCO.OH 

/OH 

^s 

^\CO.OH 

:n2ci       ( 

:H2ci      ( 

:n2ci         ( 

:H2.CN         C 

H2.CO.OH 

Dichloracetone                                                                                                        Citric  acid 

Also,  when  carefully  heated  with  concentrated  sulphuric  acid 
the  first  reaction  is  the  general  one  for  the  a-hydroxy-acids — 
the  splitting  off  of  formic  acid  (p.  171) — with  the  formation  of 
acetone-dicarboxylic  acid,  followed  by  the  decomposition  of  this 
acid  into  acetone  and  carbon  dioxide: 


POLYBASIC  ACIDS   AND   ALCOHOL-ACIDS 

CH2.CO.OH  CH2.CO.OH  CHg 

/OH 
'/ 


197 


\CO.OH 
CH2.CO.OH 


Glycollic 

Lactic 

Hydracrylic 

Glyceric 

o-Hydroxybutyric 

/3-Hydroxybutyric 

7-Hydroxybutyric 

Trihydroxy-isobutyric 

Malic 

Tartaric 

Racemic 

Mesotartaric 


Citric 


HYDROXY-ACIDS 


CH2(OH).CO.OH 
CH3.CH(OH).CO.OH 
CH2(OH).CH2.CO.OH 
CH2(OH).CH(OH).CO.OH 
CH3.CH2.CH(OH)CO.OH 
CH3.CH(OH).CH2.CO.OH 
CH2(OH).CH2.CH2.CO.OH 
(CH2OH)2.C(OH).CO.OH 
CO.OH.CH2.CH(OH).CO.OH 
CO.OH.CH(OH)  .CH(OH) .  CO.OH 
CO.OH.CH(OH).CH(OH).CO.OH 
CO.OH.CH(OH).CH(OH). CO.OH 
CO.OH 

I 
CO.OH.CH2.C.CH2.CO.OH 


Melting 
Point 

79-80° 

(Syrup) 
(Syrup) 
(Syrup) 

42-44 

(Syrup) 

(Unstable) 

116 

c.ioo0 

168-170 

205-206 

140 


153 


OH 


CHAPTER  XV 
THE  CARBOHYDRATES 

The  compounds  which  are  produced  most  abundantly,  by 
growing  plants,  and  which  are  the  most  important  products  of 
vegetation,  are  substances  which  contain  hydrogen  and  oxygen,  in 
the  proportion  in  which  they  form  water,  combined  with  carbon. 
For  this  reason  they  were  called  carbohydrates.  They  do  not  con- 
tain water  as  such,  and  they  are  in  no  sense  hydrates  of  carbon, 
as  the  name  implies.  Other  compounds  of  carbon,  hydrogen, 
and  oxygen,  in  which  the  hydrogen  and  oxygen  atoms  are  in  the 
proportion  of  two  to  one,  such  as  formaldehyde,  acetic  acid,  or 
dihydroxyl  acetone,  might  with  equal  reason  be  called  carbohy- 
drates. But,  as  in  other  cases,  the  old  name  has  been  retained, 
in  spite  of  its  erroneous  suggestion,  as  a  convenient  designation 
of  a  group  of  substances  which  are  definitely  related  to  each 
other. 

The  study  of  the  structure  of  the  carbohydrates  has  shown  that 
the  simpler  ones  are  aldehyde-alcohols  or  ketone-alcohols,  and  the 
more  complex  are  converted  into  such  compounds  by  hydrolysis. 
The  most  important  and  best  known  members  of  the  group  are 
the  sugars,  starches,  and  celluloses.  Our  knowledge  of  the  struc- 
ture of  the  sugars  has  been  greatly  extended  in  the  last  twenty- 
five  years,  especially  by  the  investigations  of  Emil  Fischer,  who 
has  succeeded  in  adding  a  considerable  number  of  new  synthetic 
sugars  to  those  found  in  nature.  The  starches  and  celluloses  are 
much  more  complex  substances  than  the  sugars  and  we  have  no 
definite  knowledge  of  their  structure  except  through  the  fact  that 
they  all  yield  simple  sugars  on  hydrolysis.  This  indicates  that 

198 


THE    CARBOHYDRATES  1 99 

they,  as  well  as  the  more  complex  sugars,  may  be  regarded  as 
anhydride-like  derivatives  of  the  simple  sugars.  Their  mole- 
cular weights  cannot  be  determined  with  any  certainty,  but  they 
appear  to  be  very  large.  Unlike  the  sugars,  they  cannot  be 
crystallized,  have  no  characteristic  taste,  and  in  some  cases  are 
entirely  insoluble  in  water. 

The  sugars,  and  the  other  carbohydrates  from  which  sugars 
are  derived  by  hydrolysis,  are  called  saccharoses  and  are  divided 
into  two  classes:  the  mono ^saccharoses,  which  do  not  undergo 
hydrolysis;  and  the  poly  saccharoses,  which  can  be  converted  by 
hydrolysis  into  monosaccharoses. 

The  Monosaccharoses 

These  sugars  have  names  that  end  in  ose.  Those  which  are 
aldehyde-alcohols  are  known  as  aldoses,  and  those  that  are  ketone- 
alcohols  are  called  ketoses.  They  are  further  distinguished  .ac- 
cording to  the  number  of  carbon  atoms  they  contain  as  dioses, 
trioses,  etc.  Except  in  one  instance,  the  rhamnose,  the  molecules 
contain  no  unsubstituted  alkyl  groups,  but  only  primary  or 
secondary  alcohol  groups  with  one  aldehyde  or  ketone  group. 
Further,  their  carbon  atoms  are  united  in  open,  unbranched 
chains,  so  that  they  are  all  derivatives  of  normal  hydrocarbons. 
When  the  aldehyde  group  is  present  it  is  a  terminal  group,  and 
the  ketone  group  is  always  next  to  a  terminal  alcohol  group. 
Compounds  of  this  structure  have  been  met  with  in  glycollic 
aldehyde  (p.  162),  glyceryl  aldehyde,  and  dihydroxyl  acetone, 
(p.  161).  These  represent  the  classes  of  dioses  and  trioses  and 
may  properly  be  included  in  the  group  of  sugars.  The  student 
will  recall  that  glycollic  aldehyde  is  "condensed"  by  the  action 
of  dilute  alkali  into  a  tetrose  (p.  162). 

All  of  the  aldoses  and  ketoses,  with  the  exception  of  glycollic 
aldehyde,  and  dihydroxyl  acetone,  contain  one  or  more  asymmetric 
carbon  atoms.  Hence  stereochemical  isomerism  is  possible, 


200  INTRODUCTION   TO    ORGANIC    CHEMISTRY 

with  an  increase  in  the  number  of  groupings  as  the  number  of 
the  asymmetric  carbon  atoms  is  greater.  The  rule  for  the  number 
of  isomers  is  given  by  the  formula  2n,  n  being  the  number  of 
asymmetric  carbon  atoms.  The  aldohexoses  contain  four  such 
atoms,  and  hence  there  are  sixteen  stereo-isomers;  the  ketohexoses 
have  three  asymmetric  carbon  atoms  and  hence  their  possible 
number  is  eight.  We  find  that  the  sugars  are  all  optically 
active  when  they  are  not  in  the  "racemic"  form. 

The  structure  of  these  compounds  is  determined  by  the  methods 
with  which  we  have  become  familiar  in  the  study  of  simpler  sub- 
stances. The  presence  of  hydroxyl  groups  and  their  number  is 
found  by  examination  of  the  acetyl  substitution  products  which 
are  obtained  when  the  sugar  is  treated  with  acetic  anhydride 
in  the  presence  of  zinc  chloride;  and  the  presence  of  the  aldehyde 
or  ketone  group  is  determined  by  the  products  of  careful  oxidation 
and  by  their  reactions.  An  aldehyde  group,  being  monovalent, 
must  always  be  at  the  end  of  the  chain  of  carbon  atoms,  and  the 
position  of  the  divalent  ketone  group  is  inferred  from  the  numbers 
of  carbon  atoms  in  the  first  oxidation  products  (cf.  p.  90). 

The  monosaccharoses  are  all  colorless  and  odorless  substances. 
They  dissolve  readily  in  water,  with  difficulty  in  absolute  alcohol, 
and  are  insoluble  in  ether.  Their  solutions  are  sweet,  and  are 
neutral  to  litmus.  Those  which  contain  five  or  more  carbon  atoms 
are  mostly  solids  which  usually  crystallize  well  from  pure  solu- 
tions, but  the  crystallization  is  often  very  slow,  and  is  retarded 
or  prevented  by  the  presence  of  other  substances.  When  heated 
above  their  melting  point,  they  are  decomposed,  turning  brown, 
and  finally  charring.  Glycerose  (glyceryl  aldehyde)  and  the 
natural  hexoses  are  fermented  by  yeast  with  the  production  of 
alcohol.  The  pentoses  do  not  enter  into  alcoholic  fermentation, 
and  the  property  of  such  fermentation  appears  to  be  restricted 
to  sugars  which  contain  three,  or  a  multiple  of  three,  carbon  atoms. 

Monosaccharoses  with  Less  than  Six  Carbon  Atoms. — 
Gly collie  aldehyde,  CH2OH.CHO,  is  the  simplest  possible  aldose; 


THE    CARBOHYDRATES  2OI 

glyceryl  aldehyde,  CH2OHCHOH.CHO,  is  the  next  aldose,  and 
dihydroxylacetone,  CH2OH.CO.CH2OH,  is  the  simplest  of  the  ke- 
tones.  Erythrose,  C4H8O4,  or  CH2OH.CHOH.CHOH.CHO,  is 
the  first  product  of  the  oxidation  of  erythritol,  the  normal  tetra- 
hydroxyl  alcohol,  and  is  probably  identical  with  the  tetrose  which 
is  formed  by  the  aldol  condensation  of  glycollic  aldehyde.  Tet- 
roses  are  also  formed  by  oxidation  of  pentonic  acid  (tetrahy- 
droxy  valeric  acid,  CH2OH(CHOH)3.(CO.OH)  in  the  form  of  its 
calcium  salt. 

Pentoses. — Arabinose  and  Xylose  are  both  aldoses  with  five 
carbon  atoms  and  have  the  formula  CH2.OH(CHOH)3.CHO. 
They  are  obtained  by  the  hydrolysis  of  natural  polysaccharoses 
— arabinose  from  gum-arabic  or  cherry  gum,  and  xylose  (wood 
sugar)  from  wood  gum,  by  boiling  beech- wood,  jute,  etc.,  with 
dilute  acids.  Rhamnose  is  a  methyl  substituted  pentose,  CH3.- 
(CHOH)4.CHO,  which  is  a  product  of  the  hydrolysis  of  certain 
glucosides. 

These  three  pentoses  are  all  dextro-rotatory.  They  are  oxi- 
dized by  bromine  to  corresponding  monocarboxylic  acids,  and 
by  nitric  acid  to  trioxyglutaric  acid,  CO.OH(CHOH)3.CO.OH. 
They  can  all  be  reduced  by  sodium  amalgam  to  the  corresponding 
pentahydroxyl  alcohols. 

Hexoses 

Two  natural  sugars,  glucose  and  fructose,  are  hexoses.  They 
are  widely  distributed  in  the  vegetable  kingdom,  occurring  to- 
gether in  the  juices  of  many  sweet  fruits,  in  the  roots,  leaves,  and 
flowers  of  plants,  and  in  honey.  These  two  sugars  are  formed  in 
equal  amounts  by  the  hydrolysis  of  cane  sugar,  and  isomers, 
identical  in  every  respect  except  in  the  matter  of  optical  activity, 
have  been  made  synthetically  from  formaldehyde  and  from 
glycerol.  They  crystallize  less  readily  than  cane  sugar.  In 
solution  both  undergo  alcoholic  fermentation  with  yeast  but  the 
rate  of  the  fermentation  is  usually  not  the  same,  and  depends 


202  INTRODUCTION  TO   ORGANIC  CHEMISTRY 

on  the  yeast  that  is  used.  Both  reduce  Fehling's  solution  to 
the  same  extent,  the  fructose  here  acting  more  rapidly  than  the 
glucose;  both  give  silver  mirrors  with  ammoniacal  silver  nitrate; 
and  neither  when  pure  is  discolored  by  cold  concentrated  sulphuric 
acid.  Their  solutions  are  both  optically  active,  glucose  being 
dextro-rotatory,  and  fructose  (levulose)  levo-rotatory.  The 
action  of  fructose  on  polarized  light  is  more  powerful  than  that 
of  glucose;  and  hence  a  solution  containing  equal  amounts  of  the 
two  sugars  (invert  sugar)  is  levo-rotatory.  (See  table  of  Specific 
Rotations  p.  408).  Both  sugars  form  compounds  with  calcium 
and  barium  when  treated  with  the  hydroxides  of  these  metals. 

d-Glucose,  CeH^Oe,  is  also  known  as  dextrose  and  grape- 
sugar.  The  name  of  dextrose  was  given  this  sugar  because  it  is 
dextro-rotatory;  but  with  the  discovery  of  other  dextro-rotatory 
hexoses,  and  of  a  levo-rotatory  glucose,  the  name  is  no  longer 
distinctive,  and  is  little  used.  Glucose  is  present  in  considerable 
quantities  in  ripe  grapes,  and  forms  the  brownish  nodules  which 
are  seen  in  raisins.  Certain  natural  substances  known  as 
glucosides  are  esters  of  glucose,  and  yield  this  sugar  as  one  of 
the  products  of  hydrolysis.  Among  these  are:  amygdalin  (p. 
147),  asculin  (in  horse-chestnut  bark),  and  the  tannins  (p.  367). 
Glucose  appears  in  diabetic  urine,  sometimes  to  the  amount  of 
8-10  per  cent. 

Formation  and  Preparation. — Glucose  is  a  product  of  the 
hydrolysis  of  a  number  of  poly  saccharoses,  which  occurs  when  they 
are  heated  with  water  with  the  addition  of  a  little  inorganic 
acid.  Starch,  dextrin,  and  maltose  can  in  this  way  be  completely 
converted  into  glucose.  Cellulose  is  soluble  in  concentrated 
sulphuric  acid,  and  when  the  solution  is  largely  diluted  with 
water  and  boiled,  soluble  carbohydrates  are  formed,  the  final 
product  of  the  hydrolysis  being  glucose.  It  is  thus  possible 
to  make  wood  and  other  vegetable  fibers  into  a  sugar,  and 
through  this  into  alcohol. 

Certain  other  carbohydrates  on  hydrolysis  yield  glucose  with 


THE   CARBOHYDRATES  203 

some  other  hexose.  Cane  sugar  gives  equal  amounts  of  dextrose 
and  levulose  (invert  sugar),  milk  sugar  is  converted  into  dextrose 
and  galactose,  and  raffinose  into  glucose,  fructose,  and  galactose. 

Glucose  may  be  prepared  in  the  laboratory  by  hydrolysis  of 
cane  sugar  in  alcoholic  solution  by  means  of  hydrochloric  acid. 
Since  glucose  is  less  soluble  in  alcohol  than  the  fructose  which  is 
simultaneously  formed,  a  considerable  part  of  it  will  crystallize 
from  the  solution. 

Commercial  glucose  or  "grape-sugar"  is  made  from  starch  by 
heating  it  with  very  dilute  acid.  In  Europe  the  starch  of  pota- 
toes, rice  and  sago  is  used  and  sulphuric  acid  is  employed  as  the 
hydrolytic  agent.  In  this  country  corn  starch  is  the  source  of 
"dextrose"  and  the  syrup  known  as  "glucose."  The  starch  is 
heated  with  a  i  to  3  per  cent,  solution  of  hydrochloric  acid, 
usually  under  pressure.  For  the  production  of  "glucose,"  the 
heating  is  stopped  when  iodine  no  longer  gives  a  blue  color  (starch) 
with  the  solution.  The  solution  is  then  nearly  neutralized  with 
sodium  carbonate,  clarified  by  bone-black  and  evaporated  in 
vacuum  pans  to  a  specific  gravity  of  1.375-1.43.  This  "glucose" 
contains  d-glucose  with  maltose,  and  considerable  amounts  of 
dextrin  which  is  an  intermediate  product.  In  the  manufacture 
of  grape-sugar,  the  heating  is  prolonged  a  little  beyond  the  point 
at  which  alcohol  fails  to  produce  a  precipitate  in  a  sample  of  the 
solution  (absence  of  starch  and  dextrin).  The  solution  is  then 
neutralized,  clarified,  and  evaporated  so  far  that  it  solidifies  on 
cooling.  Grape-sugar  forms  a  mass  of  waxy  texture,  and  con- 
tains a  small  .amount  of  dextrin.  Glucose  is  also  obtained  when 
cellulose  (wood  fiber)  is  heated  with  dilute  acids  under  pressure 
of  six  or  eight  atmospheres.  In  a  recent  process  for  making 
alcohol  from  wood  waste  such  as  saw-dust,  sulphurous  acid  is 
used  under  pressure  to  cause  the  conversion  into  glucose. 

Uses  of  "Glucose" — Glucose  is  largely  used  as  a  table  syrup, 
in  making  confectionery,  jellies,  and  preserves;  as  an  addition  to 
wine  and  beer  wort  before  fermentation  in  order  to  increase  the 


204  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

amount  of  alcohol;  as  an  adulterant  for  thick  liquids,  such  as 
extracts  of  logwood,  etc.;  and  as  a  reducing  agent  in  indigo 
dyeing. 

Properties  of  Glucose. — Glucose  crystallizes  from  water  at  or- 
dinary temperatures  with  one  molecule  of  water,  but  from  alcohol 
or  concentrated  aqueous  solutions  at  3o°-35°,  anhydrous  crystals 
are  formed  which  melt  at  146°.  It  is  much  less  sweet  than 
fructose  or  cane  sugar.  It  is  not  charred  by  concentrated  sul- 
phuric acid,  as  cane  sugar  is,  but  like  cane  sugar  is  oxidized  to 
oxalic  acid  by  nitric  acid.  Heated  with  alkalies  it  turns  brown. 

Structure. — By  the  acetyl  reaction  glucose  is  shown  to  contain 
five  hydroxyl  groups.  Reduction  by  sodium  amalgam  in  aqueous 
solution  converts  it  into  sorbitol,  a  normal  hexahydroxyl  alcohol, 
which  shows  that  the  carbon  atoms  in  glucose  are  linked  in  an 
unbranched  chain.  By  careful  oxidation  it  forms  gluconic  acid, 
C6Hi2O7  or  CH2OH(CHOH)4.CO.OH,  by  the  addition  of  one 
oxygen  atom,  which  indicates  that  glucose  contains  an  aldehyde 
group.  Gluconic  acid  cannot  be  crystallized,  as  on  concentrating 
its  solution  it  is  dehydrated  and  forms  gluconic  lactone  (cf. 
p.  172),  a  crystalline  substance  that  is  reconverted  into  glucose 
on  reduction  with  sodium  amalgam  in  slightly  acid  solution.  This 
is  a  reaction  of  great  synthetical  importance  (p.  207) .  Further  oxi- 
dation of  glucose  gives  saccharic  acid,  CeHioOs,  HO.OC(CHOH)4.- 
CO.OH.  This  is  a  dibasic  acid  and  a  comparison  of  its  formula 
with  that  of  gluconic  acid  shows  that  both  gluconic  acid  and 
glucose  contain  a  primary  alcohol  group.  We  arrive  thus  at  the 
following  constitutional  formula  for  glucose  as  an  aldose: 
CH2OH.CHOH.CHOH.CHOH.CHOH.CHO 

d-Fructose,  C6Hi2O6,  also  known  as  fruit  sugar,  and  levulose. 
We  have  seen  that  fructose  frequently  occurs  in  nature  with 
glucose,  and  is  formed  with  it  in  the  hydrolysis  of  certain  poly- 
saccharoses.  Honey  contains  about  80  per  cent,  of  invert  sugar, 
and  cane  sugar  is  completely  hydrolyzed  into  this  mixture  of 
glucose  and  fructose.  From  such  mixtures  fructose  can  be  sepa- 


THE    CARBOHYDRATES  205 

rated  in  the  form  of  an  insoluble  calcium  compound  which  yields 
fructose  when  treated  with  carbon  dioxide;  but  it  is  best  prepared 
by  the  hydrolysis  of  inulin,  a  polysaccharose  which  occurs  in  the 
tubers  of  the  dahlia  and  some  other  plants,  and  yields  only  fructose. 

Properties. — Fructose  is  somewhat  less  soluble  in  water  than 
glucose,  but  crystallizes  with  greater  difficulty.  Anhydrous 
crystals  are  obtained  from  its  alcoholic  solution  which  melt 
at  95°.  It  is  sweeter  than  glucose. 

Structure. — As  in  the  case  of  glucose,  five  hydroxyl  groups  may 
be  proved  to  be  present;  but  on  oxidation  it  gives  two  acids,  one 
with  four  carbon  atoms,  and  one  with  two,  instead  of  a  single 
acid  with  six  carbon  atoms.  When  boiled  with  mercuric  oxide  it 
gives  a  mixture  of  trihydroxy-butyric  acid  and  glycollic  acid; 
carefully  oxidized  with  nitric  acid,  it  yields  tartaric  and  glycollic 
acids: 

C6Hi2O6  +  2O  =  CH2OH.(CHOH)2.CO.OH  +  CH2OH.CO.OH 

Trihydroxy-butyric  acid  Glycollic  acid 

C6H12O6  +  40  ->  CO.OH.(CHOH)2.CO.OH  +  CH2OH.CO.OH 

Tartaric  acid  Glycollic  acid 

These  reactions  are  those  of  a  compound  with  a  ketone  struc- 
ture (p.  90)  and  show  that  fructose  is  a  ketose  with  the  formula, 
CH2OH.  CHOH.  CHOH.  CHOH.  CO.  CH2OH. 

d-Galactose,  CeH^Oe,  is  a  sugar  which  is  formed  together  with 
glucose  by  the  hydrolysis  of  milk  sugar.  A  number  of  other 
carbohydrates,  such  as  certain  gums,  also  yield  galactose  as  one 
of  the  products  of  their  hydrolysis;  and  it  is  formed  by  the  careful 
oxidation  of  dulcitol,  a  hexahydroxyl  alcohol  which  occurs  in  cer- 
tain plants.  It  is  less  soluble  in  water  than  either  glucose  or 
levulose,  and  its  solutions  are  fermented  by  yeast,  though  more 
slowly  than  those  of  these  sugars.  It  is  strongly  dextro-rotatory 
and  forms  minute  hexagonal  crystals  which  melt  at  168°. 

d-Mannose,  CeHujOe,  is  produced  together  with  fructose  by 
the  careful  oxidation  of  the  natural  hexahydroxyl  alcohol,  mannitol, 
and  is  also  formed  by  the  hydrolysis  of  certain  carbohydrates, 


206  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

especially  from  one  contained  in  vegetable  ivory.  It  is  a  hard 
amorphous  substance  which  is  hygroscopic  and  very  soluble  in 
water,  but  difficultly  soluble  in  alcohol,  even  when  hot.  It 
is  dextro-rotatory  and  readily  fermented  by  yeast. 

Both  galactose  and  mannose  are  aldoses  with  the  same  struc- 
tural formulas  as  glucose,  as  is  shown  by  their  conversion  by  careful 
oxidation  into  galactonic  and  mannonic  acids  which  are  physical 
isomers  of  gluconic  acid,  and  then  into  mucic  and  manno- 
saccharic  acids,  which  stand  in  similar  relation  to  saccharic 
acid. 

Sorbose,  CeH^Oe,  is  found  in  the  juice  of  mountain  ash  berries 
after  standing,  being  apparently  formed  by  bacterial  oxidation 
of  the  hexahydroxyl  alcohol,  sorbitol,  which  is  present  in  the 
berries.  It  is  a  ketose,  a  stereo-isomer  of  fructose. 

Formation  and  Synthesis  of  the  Monosaccharoses. — Besides 
the  method  of  formation  which  consists  in  the  hydrolysis  of 
polysaccharoses,  and  which  is  applicable  to  both  pentoses  and 
hexoses,  the  members  of  this  group  can  be  made  in  other  ways,  of 
which  the  following  are  the  most  important: 

1.  Oxidation    of    the    corresponding    polyhydroxyl    alcohols. 
The  products  obtained  by  ordinary  oxidizing  agents  (nitric  acid) 
are   aldoses,    while   the   sorbose   bacteria    (bacterium   xylinum) 
cause  the  formation  of  ketoses  not  only  from  sorbitol,  but  also 
from  glycerol  and  other  polyhydric  alcohols. 

2.  Through  the  addition  product  which  hydrocyanic  acid  forms 
with  aldehydes,  one  aldose  may  be  converted  into  another  with 
one  more  atom  of  carbon  in  the  molecule.     For  example,  an 
aldohexose    forms    with    hydrocyanic    acid    a    cyanhydrin, 

/OH 

CH2OH.CHOH.CHOH.CHOH.CHOH.CH<        .    This  is  con- 

XCN 

verted  on  hydrolysis  into  a  seven-carbon-atom  monobasic  acid, 
CH2OH.CHOH.CHOH.CHOH,CHOH.CHOH.CO.OH,  which 


THE   CARBOHYDRATES  207 

readily  loses  the  elements  of  water  with  the  production  of  a  7- 
lactone  (cf.  p.  172). 

CH2OH.CHOH.CHOH.CH.CHOH.CHOH.CO; 


and  finally,  the  lactone  in  aqueous  solution  is  reduced  by  sodium 
amalgam  to  the  corresponding  aldehyde,  which  is  an  aldoheptose, 
CH2OH(CHOH)5CHO.  By  this  method  heptoses,  octoses  and 
nonoses  have  been  prepared. 

3.  One  of  the  methods  for  descending  from  one  sugar  to  another 
with  one  less  carbon  atom  is  the  following:  the  oxime  (p.  79) 
is  made,  and  this  on  heating  with  concentrated  sodium  hydroxide 
gives   the  nitrile,   which   on  further  heating  loses  hydrocyanic 
acid  and  gives  the  lower  sugar.     The  transformations  in  the 
groups  affected  are: 

CHO  CH:N.OH        CN  CHO 

(CH.OH)4  ->  (CHOH)4   ->  (CHOH)4     ->  (CHOH)3+HCN 

I  I  I  I 

CH2OH  CH2OH  CH2OH  CH2OH 

Glucose  Oxime  Nitrile  Arabinose 

4.  The  formation  of  a  tetrose  from  glycollic  aldehyde  and  of  a 
hexose  from  formaldehyde  and  from  glyceric  aldehyde  by  aldol 
condensation  have  already  been  referred  to,  as  has  also  the 
significance  of  the  synthesis  of  a  sugar  from  formaldehyde  with 
its  suggestion  of  the  mode  by  which  the  natural  carbohydrates 
may  be  built  up  in  plants  from  the  carbon  dioxide  and  water 
(p.  86). 

5.  Aldoses  can  be  converted  into  the  isomeric  ketoses  by  means 
of  the  osazones  which  can  be  made  from  them  (see  below). 

6.  Ketoses  can  be  changed  into  the  corresponding  aldoses  by 
the  following  steps :  the  ketone  is  reduced  by  sodium  amalgam  to 
the  polyhydroxyl  alcohol;  this  may  be  converted  into  the  aldose 
by  careful  oxidation  (method  i);  or  is  oxidized  into  a  monobasic 


208  INTRODUCTION  TO   ORGANIC  CHEMISTRY 

acid  which  is  then  changed  to  the  aldose  by  the  lactone  reaction 
(method  2). 

Inactive  fructose  is  of  especial  historic  interest  as  it  is  the  first 
sugar  which  was  produced  from  substances  which  are  themselves 
capable  of  synthetic  formation.  It  results  from  the  polymeriza- 
tion of  formaldehyde  by  bases  (p.  85);  from  glyceric  aldehyde 
by  aldol  condensation;  from  glycerose  (formed  by  oxidation  of 
glycerol)  by  the  action  of  dilute  alkalies.  It  was  originally 
called  acrose.  It  has  all  the  properties  of  natural  fructose,  ex- 
cept optical  activity.  It  ferments  with  yeast,  but  the  fermenta- 
tion is  partial,  destroying  the  levo-rotatory  component  and  leav- 
ing a  dextro-rotatory  fructose. 

By  a  series  of  reactions,  mostly  of  the  kind  which  have  been 
discussed,  the  synthetic  inactive  fructose  can  be  converted  into 
the  natural  sugars  mannose,  glucose  and  fructose. 

Another  interesting  fact  is  that  glucose,  fructose  and  mannose 
are  each  partially  converted  into  both  of  the  others  under  the 
influence  of  dilute  alkalies,  an  equilibrium  being  established 
which  may  be  thus  represented; 

Glucose  <=*  Fructose  ^  Mannose 

The  study  of  the  sugars  has  been  greatly  facilitated  by  the  fact 
that  they  form  compounds  called  osazones  which,  unlike  the 
monosaccharoses  themselves,  are  sparingly  soluble  in  water,  are 
readily  obtained  in  the  pure  state  by  crystallization,  and  have 
characteristic  melting  points.  Through  these  properties  of  the 
osazones,  the  sugars,  which  by  themselves  are  separated  with 
great  difficulty,  may  be  distinguished  and  identified. 

We  have  seen  (p.  80)  that  hydrazine  and  its  derivatives  react 
with  the  aldehydes  and  ketones  to  form  hydrazones.  By  reac- 
tion with  phenyl  (C6H5)  hydrazine,  C6H6NH:NH2,  both  the 
aldoses  and  the  ketoses  form  hydrazones,  which,  when  an  excess 
of  the  phenyl  hydrazine  is  present,  react  with  it  with  the  final 


THE    CARBOHYDRATES  2OQ 

production  of  double  hydrazones  called  osazones.     The  steps  in 
the  case  of  an  aldose  are: 

-  CHOH.CHOH.CHO  +  C6H5.NH.NH2-» 

Aldose 

-CHOH.CHOH.CH:N.NH.C6H5 

Hydrazone 

-  CHOH.CHOH.CH:N.NH.C6H5  +  C6H5NH.NH2-» 

Hydrazone 

NH3  +  CeHs.NH,  +  -  CHOH.CO.CH:N.NH.C6H5, 

Carbonyl  compound 

and  this  +  C6H5.NH.NH2  -> 

-  CHOH.C.CH:N.NH.C6H5 
II 
N.NH.C6H5 

Osazone 

With  a  ketose  the  steps  are: 

-CHOH.CO.CH2OH »  -CHOH.C.CH2OH > 

Ketone  y 

N.NHC6H6 

Hydrazone 

-CHOH.C.CHO >  -CHOH.C.CH:N.NHC6H6 

II  II 

N.NHC6H5  N.NHC6H5 

Aldehyde  Osazone 

compound 

The  osazones  of  the  aldoses  and  of  corresponding  ketoses  are 
identical.  On  treatment  of  an  osazone  with  strong  hydrochloric 
acid  it  is  decomposed  with  the  formation  of  a  ketone-aldehyde, 
—  CO.CHO,  called  an  osone,  and  this  is  reduced  by  nascent 
hydrogen  into  a  ketose.  Thus  it  is  possible  to  convert  an  aldose 
into  its  isomeric  ketose,  as  for  instance,  glucose  into  fructose. 

By  the  reactions  which  have  just  been  discussed,  many  synthet- 
ical sugars  have  been  made  and  definitely  distinguished.  All 
of  the  sixteen  possible  aldolhexoses  are  known  and  five  of  the 
eight  ketohexoses,  including  the  natural  sugars.  The  synthetical 
sugars  which  have  been  made  are  stereo-isomers  of  the  natural 
sugars,  having  a  different  optical  activity  or  being  inactive.1 

1  For  further  discussion  of  the  methods  of  sugar  synthesis  and  for  the 
stereochemistry  of  the  sugars,  see:  "The  Simple  Carbohydrates  and  the 
Glucosldes"  by  E.  Frankland  Armstrong,  and  "Modern  Organic  Chemistry" 
by  C.  A.  Keane. 


210  INTRODUCTION  TO   ORGANIC  CHEMISTRY 

Stereochemistry  of  the  Hexoses. — The  configurations,  or 
stereo-formulas  of  all  of  the  possible  sixteen  aldo-hexoses  have 
been  determined  by  Fischer,  as  well  as  those  of  many  of  the 
related  alcohols  and  acids;  and  the  following  projection  formulas 
of  the  three  aldo-hexoses  which  we  have  considered,  and  of  the 
two  fructoses  (ketohexoses)  are  given  here  as  illustrations: 
d-Glucose  d-Galactose  d-Mannose 

CHO  CHO  CHO 


HCOH  HCOH  HOCH 

I  I  I 

HOCH  HOCH  HOCH 

I  I  I 

HCOH  HOCH       HCOH 

I  I  I 

HCOH  HCOH      HCOH 


CH2OH      CH2OH      CH2OH 

d-Fructose  l-Fructose 

CH2OH  CH2OH 

I  I 

CO  CO 

I  I 

HOCH  HCOH 

I  I 

HCOH  HOCH 

I  I 

HCOH  HOCH 

CH2OH  CH2OH 

In  the  systematic  nomenclature  of  sugars  which  the  synthetic 
additions  to  the  group  have  made  necessary,  all  monosaccharoses 
derived  from  a  dextro-,  levo-,  or  inactive  hexose  are  designated 
by  the  letter  d,  I,  or  i,  without  reference  to  the  rotatory  power 
they  may  actually  possess.  Thus  ordinary  fructose  which  is 
levo-rotatory  is  called  d-fructose  because  it  can  be  obtained  from 
"d-glucose."  The  same  method  of  classification  is  adopted  for  the 


THE   CARBOHYDRATES  211 

hexahydroxyl  alcohols  and  other  derivatives  of  the  hexoses. 
This  has  not  been  emphasized  in  the  brief  discussion  of  the  sugars 
in  this  book,  but  is  necessary  in  any  extended  study  of  the  litera- 
ture of  the  subject. 

The  Polysaccharoses 

We  may  divide  this  group  into  the  disaccharoses,  of  which  cane 
sugar  is  the  most  important  member,  the  trisaccharoses,  and  the 
carbohydrates  of  unknown  molecular  weight — the  starches  and 
the  celluloses — to  which  the  name  of  polysaccharoses  is  often  re- 
stricted. 

Disaccharoses 

These  sugars  have  the  molecular  formula,  Ci2H22On,  equal  to  a 
double  hexose  less  a  molecule  of  water;  and  they  are  readily  con- 
verted into  hexoses  by  hydrolysis: 

C12H22On  +  H20  =  2C6H1206 

From  the  ease  with  which  this  conversion  occurs,  it  is  inferred 
that  the  hexose  residues  in  the  disaccharoses  are  not  united  by 
the  linkage  of  carbon  atoms,  but  by  oxygen;  so  that  the  disac- 
charoses are,  in  a  sense,  anhydrides  of  the  hexoses.  They  can- 
not, however,  be  obtained  from  the  hexoses  by  means  of  water- 
withdrawing  agents,  as  many  anhydrides  are  made;  but  by  in- 
direct methods  in  which  acetyl  substitution  products  of  the 
hexoses  play  a  part,  artificial  disaccharoses  have  been  made. 

Saccharose,  sucrose,  or  cane  sugar,  Ci2H22On,  is  our  common 
sugar  and  commercially  much  the  most  important  of  all  the 
sugars.  It  is  widely  distributed  in  nature,  occurring  in  the 
juice  of  the  sugar  cane,  sorghum  and  many  other  species  of 
grass,  in  beets  and  many  other  roots,  in  the  sap  of  the  sugar 
maple  and  other  trees,  and  in  many  fruits,  and  in  seeds  such  as 
walnuts,  almonds,  and  coffee,  and  in  the  nectar  of  flowers. 
Nearly  all  of  the  world's  supply  is  obtained  from  the  sugar  cane 
and  the  sugar  beet.  In  the  growing  cane  the  only  sugar  present 


212  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

is  dextrose,  but  this  disappears  as  the  plant  matures  and  the  ripe 
cane  contains  only  a  trace  of  it  with  about  18  per  cent,  of  sac- 
charose. The  sweet  juice  is  usually  expressed  from  the  cane  by 
crushing  it  between  heavy  rolls.  Beets  contain  from  12  to  15  per 
cent,  of  sugar.  They  are  cut  into  thin  slices  or  rasped  to  a  pulp, 
and  digested  with  warm  water,  into  which  the  crystallizable 
sugar  passes  by  diffusion,  leaving  the  colloids — albuminoids,  gums 
etc.,  for  the  most  part  in  the  root  cells.  This  diffusion  process, 
consequently,  gives  a  purer  juice  than  can  be  obtained  by  other 
means.  The  subsequent  processes  are  much  the  same  in  both 
the  sugar  cane  and  the  beet  industries.  The  juice  is  boiled  with 
milk  of  lime  with  the  result  that  calcium  salts  of  the  acids  which 
are  present,  together  with  coagulated  albuminous  substances 
and  gum,  are  separated  as  a  scum.  The  clarified  juice  is  finally 
concentrated  by  evaporation,  usually  in  vacuum  pans,  allowed 
to  crystallize,  and  separated  from  the  mother-liquor  or  "molasses" 
by  draining  from  hogsheads  with  perforated  bottoms,  or  more 
commonly  by  centrifugal  machines.  The  product  is  a  raw  sugar 
of  a  more  or  less  brownish  color,  containing  a  number  of  im- 
purities. White  granulated  sugar  is  obtained  from  it  by  a  refining 
process  which  consists  essentially  in  dissolving  the  sugar  in  water, 
decolorizing-  by  bone  black  and  recrystallizing. 

The  molasses  contains  40  to  50  per  cent,  of  sugar.  This  is 
diluted,  clarified  and  boiled  down  for  a  "second  sugar."  The 
" second  molasses"  from  this  sugar,  when  obtained  from  the 
sugar  cane,  still  contains  about  40  per  cent,  of  sugar  which  it 
does  not  pay  to  recover.  It  is  sometimes  fermented  for  making 
rum  or  alcohol,  and  sometimes  used  as  fuel.  It  is  not  suitable 
for  table  use  or  cooking,  but  a  little  of  the  first  molasses  from 
cane  sugar  is  used  in  this  way.  Beet  sugar  molasses  is  unfitted  for 
table  use,  by  its  very  unpleasant  odor  and  taste  from,  the  pres- 
ence of  certain  nitrogenous  substances.  Much  of  the .  sugar  re- 
maining in  the  second  molasses  from  beet  sugar  is  recovered  by 
changing  it  into  an  insoluble  calcium  or  strontium  sucrate  by 


THE    CARBOHYDRATES  213 

treatment  with  lime  or  strontium  hydroxide.  After  separation 
and  washing,  the  sucrate  is  mixed  with  water  and  decomposed 
into  sugar  and  insoluble  calcium  or  strontium  carbonate  by 
carbon  dioxide.  The  final  molasses  from  beet  sugar  contains 
a  large  amount  of  organic  salts  of  potassium  together  with 
the  nitrogenous  substances  which  have  been  mentioned.  This 
molasses  is  usually  fermented  and  the  alcohol  distilled,  leaving 
these  substances  in  the  residue,  which  is  called  mnasse.  If  this 
is  evaporated  and  calcined,  the  ash  contains  about  35  per  cent,  of 
potassium  carbonate.  If  the  residue  from  evaporation  is  destruc- 
tively distilled,  methyl  alcohol,  ammonia  and  "trimethyl  amine" 
(p.  132)  are  obtained  as  valuable  products,  and  the  potassium 
products  are  recovered  from  the  cinder  left  in  the  retort. 

Properties. — Cane  sugar  is  soluble  in  about  half  its  weight  of 
cold  water.  It  crystallizes  well  from  concentrated  solutions 
(syrups)  in  large,  transparent  crystals  known  as  "rock-candy." 
It  melts  at  160°  and  solidifies,  on  cooling,  to  an  amorphous,  glass- 
like  mass,  which  after  a  time  becomes  crystalline.  On  stronger 
heating,  it  turns  brown,  being  converted  into  "caramel,"  an 
•amorphous  substance,  much  used  as  a  flavoring  and  coloring 
material.  At  a  high  temperature  it  is  completely  decomposed, 
with  the  evolution  of  gases  and  vapors,  leaving  a  residue  of  nearly 
pure,  porous  charcoal  (sugar  charcoal).  Among  the  products 
of  its  destructive  distillation  are  the  oxides  of  carbon,  hydro- 
carbon gases,  aldehyde,  acetic  acid,  etc.  When  moistened  and 
treated  with  concentrated  sulphuric  acid  it  turns  brown  and 
finally  chars. 

Sugar  is  oxidized  easily  by  such  agents  as  chromic  acid,  potas- 
sium chlorate,  or  nitric  acid.  With  the  first  two  the  reaction 
is  explosive;  with  concentrated  nitric  acid,  a  considerable  product 
is  oxalic  acid  (cf.  p.  177).  Caustic  alkalies  do  not  turn  cane- 
sugar  solutions  brown  as  they  do  solutions  of  dextrose. 

Cane-sugar  solutions  are  strongly  dextro-rotatory.  In  the 
presence  of  acids,  the  sugar  is  hydrolyzed  into  a  mixture  of  equal 


214  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

amounts  of  glucose  and  fructose  (invert  sugar),  which  is  levo- 
rotatory  because  of  the  stronger  optical  effect  of  fructose.  The 
hydrolysis  takes  place  slowly  in  cold  solutions  and  more  rapidly 
when  they  are  heated.  Even  carbonic  acid  effects  the  con- 
version. 

Cane  sugar  is  not  fermented  by  zymase,  the  enzyme  of  yeast, 
which  produces  alcoholic  fermentation  in  glucose  and  fructose; 
but  ordinary  yeast  causes  alcoholic  fermentation,  though  not  as 
quickly  as  with  the  hexoses,  because  it  contains  another  enzyme, 
called  invertase,  which  first  converts  the  saccharose  into  invert 
sugar.  Strong  syrups,  however,  do  not  ferment,  and  sugar  is 
used  in  the  preserving  of  fruit  and  in  jellies. 

Sugar  combines  with  various  oxides  and  hydroxides  of  metals, 
which  are  resolved  into  sugar  and  the  metal  carbonate  by  carbon 
dioxide.  The  calcium  and  strontium  sucrates,  as  has  been  noted, 
play  a  part  in  the  recovery  of  sugar  from  molasses. 

Structure  of  Saccharose. — Saccharose  is  shown  by  its  acetyl 
substitution  products  to  contain  eight  hydroxyl  groups,  and  its 
reactions  indicate  the  absence  of  aldehyde  and  ketone  groups. 
In  the  natural  synthesis  of  cane  sugar,  which  appears  to  be  effected 
from  the  hexoses,  these  groups  must  be  involved  in  the  change. 
We  have  seen  in  the  case  of  the  polyhydroxy -acids  that  lactones 
are  readily  formed  by  the  loss  of  the  elements  of  water  from  the 
carboxyl  and  -y-hydroxyl  group;  and  while  the  structure  of 
saccharose  has  not  been  definitely  established,  it  is  probable 
for  this  and  other  reasons  that  it  is  represented  by  the  following 
formula: 

O 


CH2OH.CHOH.CH.CHOH.CHOH.CH  Glucose  residue 

r°J     • 

CH2OH.CH.CHOH.CHOH.C.CH2OH  Fructose  residue 


THE   CARBOHYDRATES  215 

Lactose,  milk  sugar,  Ci2H22Oii  is  present  to  the  amount  of  3 
to  5  per  cent,  in  the  milk  of  mammals.  When  the  fats  (cream) 
have  been  removed  from  milk  and  the  casein  (curds)  has  been 
precipitated,  as  by  rennet  in  cheese-making,  the  whey  or  watery 
solution  c  ntains  most  of  the  milk  sugar,  which  is  readily  obtained 
by  evaporation,  and  purified  by  recrystallization.  It  crystallizes 
with  one  molecule  of  water,  Ci2H22On,  H2O.  It  is  much  less 
soluble,  and  much  less  sweet  than  cane  sugar.  Lactose  is  not 
affected  by  cold  concentrated  sulphuric  acid. 

Solutions  of  lactose  are  dextro-rotatory.  It  differs  from  cane 
sugar  and  resembles  dextrose  by  turning  brown  when  heated  with 
solutions  of  caustic  alkalies,  by  reducing  Fehling's  solution  and 
ammoniacal  silver  nitrate,  by  forming  a  phenyl  osazone,  and  in 
being  reduced  to  polyhydroxyl  alcohols  by  sodium  amalgam. 
It  differs  from  both  cane  sugar  and  the  hexoses  by  not  fermenting 
with  yeast.  It  is  converted  into  lactic  acid  by  the  lactic  acid 
ferment,  and  is  hydrolyzed  by  dilute  acids  into  a  mixture  of 
glucose  and  galactose,  both  of  which  are  aldoses. 

Structure. — The  reactions  of  lactose  indicate  the  presence  of  an 
aldehyde  group,  and  reasons  similar  to  those  given  for  the  con- 
stitution of  saccharose  point  to  the  following  as  the  probable 
formula  for  lactose: 

O — 

CH2OH.CHOH.CH.CHOH.CHOH.CH  Glucose  residue 

O 

CHO.CHOH.CHOH.CHOH.CHOH.CH2     Galactose  residue 

Maltose  Ci2H22On,  is  produced  from  starch  by  the  action  of 
diastase,  an  enzyme  present  in  malt,  by  an  enzyme  contained 
in  saliva,  and  by  other  ferments,  and  is  an  intermediate  product 
in  the  hydrolytic  conversion  of  starch  and  dextrin  into  dextrose. 
Its  formation  from  starch  is  a  important  factor  in  the  manufac- 
ture of  beers  and  other  alcoholic  beverages,  and  of  alcohol. 


2l6  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

Maltose  is  very  readily  soluble  in  water  and  its  solutions  are 
more  strongly  dextro-rotatory  than  those  of  any  other  sugar. 
It  reduces  Fehling's  solution,  and  is  readily  and  completely  fer- 
mented by  yeast  into  alcohol  and  carbon  dioxide.  It  forms  a 
phenyl  osazone.  From  dextrose,  which  it  so  greatly  resembles  in 
its  behavior,  it  is  distinguished  by  its  stronger  rotatory  power, 
by  being  less  soluble  in  water  and  in  alcohol,  and  by  not  reducing 
a  weak  acetic  acid  solution  of  copper  acetate.  Its  reduction  of 
Fehling's  solution,  too,  is  slower  and  less  in  amount  than  that  of 
glucose.  Maltose  yields  only  glucose  when  hydrolyzed. 

As  the  anhydride  from  two  molecules  of  an  aldose,  glucose,  it 
is  given  the  same  structural  formula  as  lactose. 

Trisaccharoses 


Raffinose,  Cigl^Oie,  is  the  only  one  of  this  group  which  has 
any  importance.  It  occurs  in  small  amounts  in  the  sugar  beet 
and  is  obtained  from  the  molasses.  It  is  also  found  in  cotton 
seed  and  in  barley.  It  is  much  less  soluble  in  water  than  cane 
sugar  and  crystallizes  with  five  molecules  of  water.  The  crystals 
lose  their  water  at  100°,  and  the  sugar  melts  atii8°-ii9°.  The 
solutions  are  strongly  dextro-rotatory.  It  is  indifferent  toward 
alkalies  and  Fehling's  solution,  but  is  completely  fermented  by 
yeast.  On  hydrolysis  it  yields  first  fructose  and  melebiose 
(melebiose  being  a  disaccharose)  which  breaks  down  into  glucose 
and  galactose. 

Two  or  three  crystallizable  carbohydrates  obtained  from 
various  roots  seem  to  belong  between  the  well-characterized  sugars 
and  the  amorphous  carbohydrates  of  much  higher  molecular 
weight.  Their  molecular  weights  are  not  known  with  certainty 
but  are  possibly  expressed  in  the  formula  CaeH^Oai.  They 
are  readily  soluble  in  water,  are  dextro-rotatory  and  give  mixtures 
of  sugars  on  hydrolysis. 


THE    CARBOHYDRATES  217 

Carbohydrates  of  Unknown  Molecular  Weight 
Polysaccharoses 

Most  of  these  carbohydrates  are  amorphous  substances  and  have 
no  distinctive  taste.  The  most  important  members  of  the  group 
—  the  starches  and  celluloses  —  are  insoluble  in  water,  and  those 
which  appear  to  dissolve  form  "  colloidal  solutions."  Like  other 
amorphous  and  colloidal  substances  they  have  no  definite  melting 
points.  Their  composition  is  represented  by  the  formula 
CeHioOs,  but  their  molecular  weights  are  unknown  though  there 
is  evidence  that  they  must  be  very  large.  The  formula  usually 
given  them  is,  therefore  (CeHioOs)  . 

Since  these  carbohydrates  give  simple  sugars  on  hydrolysis,  we 
may  infer  that  they  are  built  up  of  monosaccharose  residues 
united,  as  in  the  disaccharoses,  by  linking  oxygen  atoms.  If 
this  is  the  case  their  relation  to  the  simple  sugars  would  be 
represented  by 

xC6Hi2O6  -  (x-i)H2O 


It  would  be  practically  impossible  to  determine  by  analysis 
the  differences  between  the  composition  represented  by  this  last 
formula  and  that  shown  by  (CeHioOs)*,  if  x  is  very  large.  For 
instance,  if  x  =  100,  the  percentages  of  carbon,  hydrogen,  and 
oxygen  corresponding  to  the  two  formulas  would  be: 

For  (C6HioO6)ioo  For  C60oHioojO60i 

C  =  44.42  44.37 

H  =    6.22  6.23 

O  =  49-36  49-40 

100.00  100.00 

Most  of  these  carbohydrates  are  the  products  of  plant  life, 
£nd  together  with  the  natural  sugars  are  built  up  from  the  carbon 
dioxide  of  the  air  and  water,  probably  through  the  formation  of 


2l8  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

formaldehyde  and  subsequent  polymerizations.  Cane  sugar  ap- 
pears to  be  the  first  definite  carbohydrate  formed  which  can  be 
isolated,  though  fructose,  glucose,  and  maltose  are  also  present 
in  the  green  leaf.  The  more  complex  starches  and  celluloses 
are  the  final  products  of  the  plant  synthesis. 

Starch  occurs  in  nearly  all  plants,  and  is  utilized  by  the  plant 
for  the  elaboration  of  other  substances.  It  is  stored  in  consider- 
able quantities  in  the  seeds,  tubers,  and  many  roots,  where  it 
forms  an  important  reserve  material  for  the  nourishment  of  the 
future  plant  until  it  can  become  self-supporting  from  atmospheric 
supplies. 

The  chief  industrial  sources  of  starch  are  potatoes,  wheat, 
corn,  rice,  arrowroot  and  certain  palms.  In  this  country  corn 
and  wheat  are  used;  in  Europe,  potatoes,  rice  and  wheat  are  mainly 
employed.  The  manufacture  of  starch  is  essentially  a  mechanical 
separation  from  the  gluten,  fats,  etc.,  which  accompany  it  in  the 
original  material.  In  making  corn  starch,  for  instance,  one  proc- 
ess is  in  outline  as  follows:  Much  of  the  oil  is  removed  and  the 
gluten  softened  by  first  steeping  in  warm  water  for  some  days. 
Next,  the  grain  is  ground,  while  a  current  of  water  carries  the 
product  to  revolving  sieves  and  then  to  bolting  cloth  strainers, 
through  which  the  starch  passes  in  suspension  in  the  water.  On 
standing,  the  crude  starch  is  deposited,  and  after  being  washed 
with  fresh  water  is  stirred  up  in  vats  with  a  dilute  solution  of 
caustic  soda.  After  several  hours  the  suspended  matters  are 
allowed  to  settle,  and  the  solution  containing  much  of  the  im- 
purity is  drawn  off.  The  sediment  is  again  stirred  up  with  water, 
and  allowed  to  stand  until  the  gluten  is  deposited,  while  the 
starch,  still  in  suspension,  is  drawn  off  and  deposited  in  other 
tanks.  By  several  repetitions  of  this  process  the  starch  is  mostly 
removed  from  the  gluten  and  at  the  same  time  separated  into 
several  grades.  Modifications  of  this  process  are  also  employed, 
and  centrifugal  machines  are  sometimes  used  to  separate  the 
starch  from  the  wash  water.  Corn  contains  about  58  per  cent. 


THE   CARBOHYDRATES  2 19 

of  starch  and  about  50  per  cent,  is  actually  obtained,  and,  at 
the  same  time,  over  20  per  cent,  of  gluten  suitable  for  cattle 
food. 

Properties. — Starch  is  a  white,  glistening  powder,  consisting 
of  micr  .scopic  granules  which  have  a  concentric  structure  and 
are  doubly  refracting.  The  form,  size  and  markings  of  the 
granules  vary  with  the  source,  so  that  this  is  readily  determined 
by  a  microscopical  examination. 

Starch  is  very  hygroscopic,  and  ordinary  starch  contains  from 
16-18  per  cent,  of  water,  which  can  be  driven  off  by  careful  heating 
up  to  110°.  The  granules  are  enveloped  in  a  cellulose  membrane 
which  completely  protects  them  from  the  action  of  cold  water, 
but  when  heated  with  water  the  granules  swell  up  and  burst, 
forming  starch  paste,  and  on  longer  heating  some  of  the  starch 
goes  into  colloidal  solution.  If  treated  for  some  days  with  a  cold 
dilute  inorganic  acid,  "soluble  starch"  is  produced  which  dis- 
solves in  hot  water  without  forming  a  paste. 

When  heated  to  2oo°-25o°  starch  is  changed  into  dextrin,  and 
a  similar  change  is  effected  at  a  lower  temperature,  when  the 
starch  has  first  been  moistened  with  hydrochloric  or  nitric  acid, 
dried  at  50°,  and  then  heated  to  140°-! 70°.  Starch  is  hydrolyzed 
to  dextrin,  maltose,  and  glucose,  by  dilute  acids,  and  also  by 
diastase,  an  enzyme  contained  in  barley  sprouts,  and  by  ptyalin, 
the  characteristic  enzyme  of  saliva.  It  does  not  form  an  -osazone, 
and  its  solutions  do  not  reduce  Fehling's  solution  or  ferment  with 
yeast. 

Starch  is  readily  detected  by  the  intense  blue  color  which  it 
gives  when  brought  in  contact  with  free  iodine.  The  nature  of 
this  "  starch  iodide,"  is  not  known.  It  usually  contains  18  to 
20  per  cent,  of  iodine. 

Uses. — Starch  is  a  very  important  food,  both  in  natural  sub- 
stances and  when  prepared  from  them,  being  first  hydrolyzed 
and  then  supplying  the  chief  fuel  material  for  the  maintenance 
of  the  temperature  of  the  body.  It  is  used  in  the  preparation  of 


220  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

glucose  and  dextrin,  and  is  employed  in  laundry  work,  in  finish- 
ing cotton  cloth,  in  sizing  paper,  for  making  paste,  etc.  Different 
starches  vary  in  their  properties  to  some  extent  and  are  adapted 
to  different  purposes.  Sago,  tapioca,  arrowroot,  and  some  other 
starches  are  used  chiefly  for  food.  Wheat  starch  makes  the  best 
paste,  rice  starch  is  preferred  for  toilet  powders,  while  potato 
and  corn  starch  are  most  largely  employed  in  the  glucose  and 
dextrin  industries,  and  are  also  used  for  other  purposes. 

Inulin  (CeHioOs)*,  occurs  in  many  composite  and  some  other 
plants  in  a  swollen  or  dissolved  state.  It  differs  from  ordinary 
starches  by  being  readily  soluble  in  warm  water,  and  giving 
solutions  which  are  not  colored  by  iodine,  and  do  not  form  a 
jelly.  The  solutions  are  levo-rotatory,  and  the  inulin  is  easily 
hydrolyzed  by  dilute  acids  with  the  formation  of  fructose  as 
the  sole  product  (cf.  p.  204).  Inulin  is  not  affected  by  diastase. 
When  dried,  it  forms  a  white  powder,  consisting  of  minute 
spherical  granules.  * 

Glycogen  (CeHioOs)*,  is  a  starch-like  substance  found  in  the 
animal  organism,  being  especially  abundant  in  the  liver.  It 
also  occurs  in  mollusca,  and  in  moulds  and  other  fungi.  It 
resembles  starch  in  appearance,  but  dissolves  in  warm  water  to 
an  opalescent  solution  from  which  it  can  be  precipitated  by 
alcohol.  Its  solutions  are  colored  red  by  iodine.  They  are 
dextro-rotatory,  and  are  hydrolyzed  by  acids,  and  by  diastase 
and  ptyalin,  into  the  products  similar  to  those  given  by  starch. 

Dextrin  is  produced,  as  already  stated,  when  starch  is  heated 
alone,  or  after  it  has  been  moistened  with  acids.  It  is  of  a 
brownish  color,  which  is  lighter  when  the  acid  process  is  used; 
but  in  this  case  the  dextrin  contains  some  sugar  and  its  adhesive 
power  is  less.  It  is  also  the  first  product  of  the  hydrolysis  of 
starch.  Dextrin  is  readily  soluble  in  water  and  is  precipitated 
from  its  solutions  by  alcohol.  The  solutions  reduce  Fehling's 
solution,  and  give  a  red  to  violet  color  with  iodine.  They  are 
dextro-rotatory  and  are  hydrolyzed  to  maltose  and  glucose. 


THE   CARBOHYDRATES  221 

Dextrin  is  not  directly  fermentable  by  yeast.  It  is  used  for 
making  mucilage,  and  is  also  employed  in  calico  printing  and 
tanning  to  thicken  the  colors  and  extracts,  in  brewing  and  in 
confectionery. 

GuiuS. — This  name  is  given  to  certain  products  of  plants  which 
sometimes  occur  as  translucent  amorphous  masses,  and  in  other 
cases  are  precipitated  from  alkaline  extracts  of  plant  substances 
by  hydrochloric  acid  and  alcohol.  They  go  into  colloidal  solu- 
tion in  water,  forming  sticky  liquids,  and  are  precipitated  from 
these  solutions  by  alcohol.  They  appear  to  be  mixtures,  but 
contain  certain  carbohydrates,  which,  unlike  any  we  have  so 
far  considered,  often  yield  pentoses  on  hydrolysis.  Gum  arabic, 
and  the  gums  which  appear  on  cherry  and  peach  trees,  give 
arabinose;  xylan,  a  gum  frequently  found  in  tree  bark,  and  a  gum 
obtained  from  grains,  give  xylose.  Galactose  is  formed  at  the 
same  time  in  most  cases. 

Cellulose  forms  the  cell  membrane  in  all  plants,  and  is  their 
chief  solid  constituent.  It  is,  however,  almost  always  incrusted 
with  other  substances  (lignin,  resins,  etc.).  These  substances 
can  be  removed  more  or  less  completely  by  treatment  with 
various  reagents  which  act  on  them  more  readily  than  on  the 
cellulose.  Thus  paper  pulp  is  made  from  wood,  and  the  textile 
fibers  of  linen,  hemp,  and  jute  are  prepared  by  a  bacterial  fer- 
mentation in  water  ("retting")  which  softens  and  partly  destroys 
the  gummy  and  resinous  matters.  Cotton,  linen,  and  various 
piths  are  almost  pure  cellulose,  and  the  best  "washed"  filter 
paper  is  cellulose  with  only  a  trace  of  impurity. 

Properties. — Cellulose  is  a  stable  substance,  insoluble  in  all 
ordinary  solvents;  but  it  is  dissolved  by  an  ammoniacal  solution 
of  copper  hydroxide  ("Schweitzer's  reagent"  made  by  forcing  a 
current  of  air  through  a  solution  of  ammonia  in  which  copper 
turnings  are  placed) ;  and  is  precipitated  from  this  solution  by 
acids  and  salts.  The  precipitated  cellulose,  when  washed  with 
alcohol  and  dried,  forms  a  white  amorphous  powder.  A  water- 
proof paper  can  be  prepared  by  passing  unsized  paper  through 


222  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

a  strong  solution  of  Schweitzer's  reagent  and  then  pressing 
several  sheets  together  without  washing. 

Strong  sulphuric  acid  (4:1)  dissolves  cellulose,  and  if  the  fresh 
solution  is  poured  into  water  a  colloidal  substance  is  precipitated, 
which,  so  long  as  it  is  in  contact  with  the  acid,  is  colored  blue  by 
iodine,  as  starch  (amylum)  is,  and  is  hence  called  amyloid.  The 
blue  color  also  appears  when  cellulose  is  moistened  with  a 
solution  containing  free  iodine  (iodine  in  potassium  iodide) 
and  then  treated  with  concentrated  sulphuric  acid  or  zinc 
chloride  solution  (test  for  cellulose).  "Parchment  paper"  is 
paper  coated  with  amyloid  by  dipping  unsized  paper  into  sul- 
phuric acid  (4:1)  and  washing  it  immediately  with  water.  A 
strong  solution  of  zinc  chloride  acts  in  the  same  way  as  sulphuric 
acid. 

If  the  colloidal  solution  of  cellulose  in  sulphuric  acid  is  allowed 
to  stand  for  some  time  before  diluting  it,  and  is  then  boiled,  solu- 
ble carbohydrates  are  formed,  among  which  glucose  is  usually 
present  in  considerable  quantity. 

Dilute  alkalies  do  not  affect  cellulose,  but  strong  solutions 
form  compounds  which  are  decomposed  when  washed  with  water, 
leaving  a  hydrate  of  cellulose.  When  cotton  cloth  is  treated  in 
this  way  (under  tension  to  prevent  shrinking)  the  fibers  acquire  a 
silky  luster,  and  the  cloth  is  known  as  "mercerized"  cotton.1 

When  the  compound  formed  by  the  action  of  the  alkali  on 
cellulose  is  treated  with  carbon  disulphide  it  produces  a  substance, 
cellulose  xanthate  (p.  243)  which,  when  beaten  with  water, 
forms  a  thick  solution  known  as  "viscose."  This  is  easily  de- 
composed with  the  formation  of  a  cellulose  hydrate.  By  squirting 
viscose  through  fine  tubes  into  a  solution  which  causes  this  decom- 
position, lustrous  threads  of  artificial  silk  are  formed.  Artificial 
silks  are  also  made  from  nitrocellulose,  and  by  treatment  of 
cellulose  with  ammoniacal  copper  solutions.  Viscose  is  also 
employed  in  making  photographic  films,  in  sizing  paper,  and 
for  other  purposes. 

The  presence  of  alcohol  groups  in  cellulose  can  be  proved  by  the 

1  Process  discovered  by  John  Mercer  about  1850. 


THE   CARBOHYDRATES  223 

usual  method.  It  can  therefore  form  esters,  and  among  the 
esters  of  cellulose  is  a  cellulose  triacetate  which  on  evaporation  of 
its  chlor  form  or  other  solution  leaves  a  tough  water  -proof  film. 
Such  films  are  non-inflammable  and  used  in  photography,  for 
water-proofing,  insulation  of  wires,  etc.  The  esters  which  are 
formed  by  reaction  with  nitric  acid  are,  however,  the  most  im- 
portant ones.  The  number  of  acid  radicals  introduced  depends 
on  the  strength  of  the  acid  used,  the  temperature,  and  the  time 
allowed  the  reaction.  These  esters  are  called  "  nitrocelluloses," 
just  as  the  glyceryl  nitrate  is  called"  nitroglycerine."  A  mixture 
of  the  lower  nitrates,  in  which  two  to  five  nitric  acid  radicals 
have  replaced  hydroxyl  in  Ci2H2oOio  is  called  "pyroxylin"  and 
its  solution  in  alcohol  and  ether  is  "collodion."  "Celluloid"  is 
an  intimate  mixture  of  pyroxylin  with  camphor.  These  sub- 
stances burn  with  a  quick  flare,  but  are  not  definitely  explosive. 
When  cellulose  is  nitrated  further  by  means  of  a  mixture  of  con- 
centrated nitric  and  sulphuric  acids  the  explosive  hexanitrate  is 
produced  [C^H^O^NOsJelx-  This  is  used  in  making  smokeless 
powder.  "Gun-cotton"  made  by  this  treatment  from  cotton 
fiber  resembles  closely  in  appearance  the  cotton  from  which  it  is 
made.  It  is  insoluble  in  alcohol  and  ether  as  well  as  in  water. 
It  burns  rapidly  but  without  explosion,  when  unconfined.  When 
confined,  it  explodes  violently  on  detonation.1 

Storage  of  Energy  in  Plants.  —  In  connection  with  this  study  of 
carbohydrates,  the  amount  of  energy  stored  by  plants  in  the  form 
of  carbohydrates  is  of  interest.  In  the  building  up  of  the  amount 
of  these  substances  which  is  represented  by  the  gram-molecular 
weight  of  the  simple  composition  formula  of  starch  or  cellulose 
(162  grams),  about  670  large  calories  are  required.  Roughly 
indicated,  the  change  is  shown  as  follows: 


6CO2  +  sH20  =  CeHioOs  +  6O2  -  670  calories 

The  necessary  energy  for  this  process  comes  from  sunlight,  which 
1  See  J.  B.  Bernadou,  "Smokeless  Powder,  Nitrocellulose,  etc." 


224  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

is  the  source  of  almost  all  of  the  energy  at  man's  disposal,  since 
that  obtained  from  water  power  and  wind  is  also  the  result  of 
solar  radiation.  The  storage  of  energy  in  the  formation  of  car- 
bohydrates, it  should  be  noted,  is  not  only  through  the  synthesis 
of  these  substances,  but  also  in  the  release  of  oxygen  with  its 
potential  chemical  energy.  In  the  various  processes  of  utiliza- 
tion of  this  energy,  in  the  use  of  fuels,  of  food,  etc.,  the  potential 
energy  of  the  organic  materials  and  of  oxygen  .is  transformed  into 
kinetic  energy  which  largely  appears  as  heat. 

Fermentation  and  Enzymes1 

The  term  fermentation  originally  signified  the  effervescent 
action  which  occurs  when  sugars  are  converted  into  alcohol  by 
yeast.  It  has  since  come  to  include  a  great  variety  of  changes 
in  which  more  or  less  complex  organic  substances  are  resolved 
into  simpler  ones  under  the  influence  of  certain  living  organisms 
or  of  substances  contained  in  them.  While  it  was  long  believed 
that  the  living  yeast  cells  were  essential  to  the  process  of  alcoholic 
fermentation,  other  changes,  like  that  of  starch  into  glucose  by 
means  of  malt,  were  found  to  be  due  to  "unorganized  ferments" 
or  substances  which,  like  the  diastase  in  malt,  are  not  living 
organisms,  though  formed  by  such  organisms.  Such  unorganized 
or  "unformed"  ferments  are  known  as  enzymes.  The  inversion 
of  cane  sugar  which  is  effected  by  yeast  before  alcoholic  fermen- 
tation sets  in  is  effected  by  such  an  enzyme  known  as  invertase. 
In  1898  Buchner  demonstrated  that  the  living  yeast  was  not 
necessary  for  alcoholic  fermentation,  but  that  this  change  can 
be  brought  about  by  means  of  a  substance  in  the  juice  expressed 
from  yeast  and  freed  from  all  living  organisms.  This  enzyme  is 
called  zymase. 

The  present  view  in  regard  to  all  the  reactions  which  are  classed 
as  fermentations  is  that  they  are  the  result  of  the  action  of 

1  See  W.  M.  Bayliss,  "The  Nature  of  Enzyme  Action,"  and  Cohnheim, 
"  Enzymes." 


THE  .CARBOHYDRATES  225 

enzymes  which  probably  act  as  catalytic  agents.  Some  of  them 
cause  the  splitting  of  the  complex  substance  into  simpler  ones, 
as  in  the  jreaking  down  of  glucose  into  alcohol  and  carbon  dioxide; 
others  bring  about  hydrolysis,  as  in  the  conversion  of  starch 
into  glucose  by  diastase,  and  the  production  of  various  hexoses 
from  the  disaccharoses;  others,  still,  effect  oxidations  with  the 
aid  of  the  oxygen  of  the  air,  as  in  the  fermentation  processes  by 
which  acetic  acid  is  formed  from  alcohol,  and  lactic  and  butyric 
acids  from  sugars.  Certain  reductions,  also,  are  apparently  the 
result  of  enzymic  action. 

The  enzymes,  like  other  catalyzers,  show  a  very  definite  select- 
ive power  in  their  action.  We  have  had  a  number  of  instances 
showing  this  fact,  and  may  recall  as  an  illustration  the  destruc- 
tion of  one  of  the  two  optically  active  components  in  racemic  acid 
by  certain  bacteria,  while  the  other  is  untouched  (p.  192).  The 
enzymes  are  probably  asymmetric  substances,  and  we  may 
imagine  that  that  selective  action  is  due  to  some  relation  between 
their  (unknown)  structure  and  that  of  the  compound  on  which 
they  act.  As  Emil  Fischer  suggests,  the  enzymes  and  the  com- 
pounds may  possess  complementary  configurations  like  those 
of  a  lock  and  its  key. 

None  of  the  enzymes  have  been  obtained  in  a  state  of  complete 
purity.  They  are  very  complex  substances  of  a  protein  character, 
and  efforts  to  isolate  them  from  the  other  proteins  with  which 
they  are  associated  cause  a  loss  of  their  activity.  They  occur 
chiefly  in  moulds,  yeasts,  bacteria,  and  living  tissues,  and  these 
organisms  are  usually  employed  to  bring  about  the  fermentations 
without  attempting  to  separate  the  enzymes  from  them.  In  a 
few  instances,  powders  are  prepared  which  contain  the  enzymes, 
such  as  diastase,  pepsin,  and  rennin. 

While  some  of  the  reactions  which  are  effected  by  enzymes  can 
also  be  brought  about  by  inorganic  catalyzers  (notably  those  of 
hydrolysis  of  sugars,  starch,  and  glucosides),  and  alcohol  can 
readily  be  converted  into  acetic  acid  by  ordinary  oxidizing 


226  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

agents,  many  other  transformations,  such  as  the  production  of 
alcohol  and  of  lactic  acid  from  sugars,  cannot  be  realized  by  the 
usual  chemical  means.  Very  many  of  the  chemical  changes 
which  go  on  in  living  plants  and  animals  are  now  known  to  be 
dependent  on  the  presence  of  enzymes. 

We  have  spoken  of  enzymes  as  catalytic  agents.  They  at 
least  resemble  them,  as  appears  from  the  facts  that,  like  the  in- 
organic catalysts,  they  are  not  used  up  in  the  processes  which  they 
conduct,  they  do  not  enter  into  the  products  of  the  reactions, 
and  their  amount  in  proportion  to  the  quantity  of  substance 
transformed  is  often  infinitesimally  small.  It  is  probable  that 
no  catalyst  is  capable  of  starting  a  reaction;  but  that  it  acts  rather 
as  an  accelerator  of  actions  which  are  already  proceeding,  though 
often  with  such  slowness  that  we  are  quite  unable  to  note  their 
progress. 

It  is  believed  that  enzymes,  or  substances  of  the  nature  of 
enzymes,  are  generated  abundantly  in  the  tissues  of  both  plants 
and  animals,  and  that  the  secretions  which  are  so  intimately 
associated  with  digestion  and  other  functions  of  the  body  owe 
their  special  effectiveness  to  the  presence  of  these  substances. 


CHAPTER  XVI 
DERIVATIVES  OF  CARBONIC  ACID 

Carbonic  acid,  CO  (OH)  2,  which  is  assumed  to  be  present  in 
solutions  of  carbon  dioxide,  carbon  dioxide  its  anhydride,  and 
the  carbonates,  are  always  treated  in  inorganic  chemistry;  but  these 
compounds,  as  well  as  carbon  monoxide,  belong  also  to  organic 
chemistry  if  we  define  it  broadly  as  the  chemistry  of  the  com- 
pounds of  carbon.  As  these  compounds  have  been  sufficiently 
presented  in  inorganic  chemistry,  it  is  only  necessary  for  us  here 
to  recall  the  part  which  they  play  in  the  synthesis  of  some  organic 
compounds  and  to  call  attention  to  the  fact  that  carbonic  acid  may 
be  regarded  as  hydroxyl  formic  acid,  HO. CO. OH,  and  may 
indeed  be  reduced  to  formic  acid  (and  carbonates  to  formates). 

There  are  certain  compounds,  however,  which  may  be  regarded 
as  derivatives  of  carbonic  acid,  in  the  sense  in  which  this  term 
has  been  employed,  and  which  from  their  character  are  usually 
classed  with  the  organic  substances.  Some  of  these  compounds 
are  briefly  discussed  in  this  chapter  by  themselves,  because  of  the 
unusual  character  of  carbonic  acid  as  compared  with  other 
organic  acids. 

Carbonyl  chloride,  COC12,  may  be  considered  as  the  dichloride 
of  carbonic  acid.  It  is,  in  fact,  formed,  though  in  small  amount, 
by  the  action  of  phosphorus  pentachloride  on  sodium  carbonate, 
just  as  chlorides  of  other  organic  acids  are  from  their  salts.  It 
is  also  formed  from  carbon  tetrachloride  when  this  is  heated 
with  sulphur  trioxide  or  phosphorus  pentoxide;  and  when  a 
mixture  of  carbon  dioxide  and  carbon  tetrachloride  vapor  is  led 
over  pumice  heated  to  350°: 

C02  +  CC14  =  2COC12 

227 


228  INTRODUCTION  TO   ORGANIC  CHEMISTRY 

It  is  also  one  of  the  products  of  the  oxidation  of  chloroform 
(cf.  p.  39);  and  carbon  monoxide  and  chlorine  unite  directly  under 
the  influence  of  sunlight  to  carbonyl  chloride.  The  compound 
was  first  obtained  in  this  way  and  was  given  the  name  of 
phosgene,  as  a  product  formed  by  the  action  of  light. 

Carbonyl  chloride  is  prepared  commercially  by  passing  a 
mixture  of  chlorine  and  carbon  monoxide  over  charcoal,  which 
acts  as  a  catalyzer. 

Carbonyl  chloride  is  a  gas  (boiling  point  8.2°)  which  dissolves 
readily  in  benzene  and  toluene.  It  has  a  stifling  odor,  and  is 
very  irritating  to  the  throat  and  lungs.  It  is  sold  in  liquid  form 
in  cylinders  and  in  solution  in  toluene,  and  is  employed  in  synthet- 
ical work,  both  in  laboratories  and  in  the  making  of  coal  tar 
dyes. 

Reactions. — Carbonyl  chloride  gives  the  reactions  which  are 
characteristic  of  acyl  chlorides  with  water,  alcohol,  and  am- 
monia (cf.  p.  115);  but  in  some  respects  is  a  more  powerful  agent 
than  acetyl  chloride,  as  is  seen  by  the  fact  that  it  reacts  with 
acetic  acid  at  120°  with  the  production  of  acetyl  chloride,  and 
converts  the  sodium  salts  of  the  fatty  acids  into  their  acid 
anhydrides. 

A  monochloride  of  carbonic  acid  would  be  chloroformic  acid, 
C1CO.OH;  but  this,  like  formyl  chloride,  HCO.C1,  has  not  been 
obtained.  Both  these  compounds,  if  formed,  must  be  very  un- 
stable, breaking  down  into  hydrogen  chloride  and  carbon  dioxide 
or  carbon  monoxide. 

Esters  of  Carbonic  Acid. — By  the  action  of  alcohols  on  car- 
bonyl chloride,  esters  are  formed.  The  first  product  is  an  ester 
of  chlorcarbonic  (or  chlorformic)  acid: 

C1CO.C1  +  C2H5OH  =  C1CO.OC2H6  +  HC1 

By  further  action  of  alcohol  or  of  alkali  alkoxide  on  the  chlor- 
carbonic ester,  the  neutral  ester,  CO(OC2H6)2,  is  produced.  In 


DERIVATIVES    OF    CARBONIC   ACID  2 29 

this  way  both  simple  esters,  and  mixed  esters,  such  as  CH3O.CO.- 
OC2H5,  can  be  made. 

The  chlorcarbonic  esters  are  liquids  of  tear-compelling  odor. 
They  are  used  in  synthetic  reactions  for  the  purpose  of  introducing 
the  carboxyl  group.  For  instance,  by  reaction  with  the  sodium 
compound  of  ethyl  malonic  ester  (cf.  p.  181),  ethyl  chlorcarbonate 
gives  the  ethyl  ester  of  methane-tricarboxylic  acid. 

CHNa(CO.OC2H5)2   +    C1CO.OC2H5    =    CH(CO.OC2H5)3    + 

NaCl 

In  many  reactions  these  esters  split  into  carbon  dioxide  and  the 
alkyl  chloride;  e.g.,  with  ZnCl2: 

C1CO.OC2H5  =  C02  +  C2H5C1; 

and  by  nascent  hydrogen  they  are  converted  into  esters  of  formic 
acid. 

The  neutral  esters  are  liquids  of  ethereal  odor,  insoluble  in  water, 
and  readily  saponified.  When  heated  with  an  alcohol  which 
contains  a  higher  alkyl  group,  this  is  substituted  for  the  lower  one 
in  the  ester: 

CH3O.CO.OC3H7  +  C3H7OH  =  CO(OC3H7)2  +  CH3OH 

Acid  esters  of  carbonic  acid,  such  as  C2H5O.CO.OH,  are  too 
unstable  to  exist,  but  their  alkali  salts,  C2H5O.CO.ONa,  are  formed 
by  leading  carbon  dioxide  into  an  alcoholic  solution  of  an  alkoxide. 
These  ester-salts  are  decomposed  by  water  with  the  production 
of  alcohol  and  alkali  carbonate. 

Amides  of  Carbonic  Acid 

As  in  the  case  of  the  carbonic  acid  chlorides,  the  diamide  is  a 
stable  compound  while  the  monamide  cannot  be  isolated. 

Carbamic  acid,  NH2.CO.OH,  the  monamideof  carbonic  acid, 
exists  only  in  its  salts,  esters,  and  chloride.  Ammonium  car- 


230  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

bamate,  the  ammonium  salt  of  the  monamide,  NH2CO.ONH4,  is 
formed  when  carbon  dioxide  and  ammonia  gas  are  brought  to- 
gether. Commercial  ammonium  carbonate,  which  is  prepared 
by  sublimation  from  a  mixture  of  ammonium  sulphate  and  cal- 
cium carbonate,  contains  both  ammonium  carbamate  and  acid 
ammonium  carbonate.  The  carbamate  is  precipitated  when 
ammonia  and  carbon  dioxide  are  led  into  cool,  absolute  alcohol, 
and  may  be  prepared  in  this  way.  In  solution  in  water  it  is 
partly  converted  into  the  carbonate: 


/ONH4 
CO  +  H20  =  CO 

\)NH4  \)NH4 

Acids  decompose  it  into  carbon  dioxide  and  the  ammonium 
salts  of  the  acid: 

NH2CO.ONH4  +  2HC1  =  2NH4C1  +  CO2 

At  60°,  the  solid  carbamate  breaks  up  into  ammonia  and  carbon 
dioxide;  and  when  it  is  heated  in  sealed  tubes  to  130°  —  140°, 
it  is  largely  converted  into  urea: 

NH2.CO.ONH4  =  NH2.CO.NH2  -f  H2O 

Urea,  CO(NH2)2,  was  discovered  in  urine  in  1773,  and  is  of 
great  physiological  interest  as  it  is  the  most  important  nitrogen 
end-product  of  the  metabolism  of  protein  substances  in  man  and 
the  carnivora.  The  average  amount  of  urea  excreted  by  an  adult 
person  in  health,  is  about  30  grams  a  day,  representing  about  84 
per  cent,  of  the  total  nitrogen  eliminated  from  the  system. 
In  disease,  the  proportions  of  urea  and  other  nitrogen  compounds 
may  be  markedly  different. 

Preparation  from  Urine.  —  Urea  may  be  obtained  from  urine  in 
the  form  of  its  nitrate  by  evaporating  the  urine  to  small  bulk 
and  adding  nitric  acid,  Urea  nitrate,  CO(NH2)2.HN03,  is 


DERIVATI/ES   OF   CARBONIC  ACID  23! 

precipitated,  and  purified  by  oxidizing  agents  (nitric  acid  or  potas- 
sium permanganate)  and  recrystallization.  Urea  is  set  free 
from  the  nitrate  by  decomposing  the  salt  in  a  warm  solution  with 
barium  carbonate.  On  evaporating  the  solution  of  urea  and 
barium  nitrate  to  dryness  and  extracting  with  hot  alcohol,  the 
urea  alone  is  dissolved. 

Formation  and  Preparation  from  Other  Substances.  —  i.  Urea  was 
first  made  in  the  laboratory  by  Wohler  in  1828.  He  obtained 
it  as  a  result  of  evaporating  an  aqueous  solution  of  ammonium 
cyanate: 


NH2 

Ammonium  cyanate  (p.  150)  had  not  then  been  prepared  from  its 
elements,  but  it  was  considered  to  be  essentially  an  inorganic  sub- 
stance. Up  to  this  time  no  organic  substance  had  been  made 
from  inorganic  material  and  it  had  been  generally  thought  that* 
transformations  of  this  sort  were  impossible.  Wohler's  discovery 
is,  therefore,  of  great  historical  importance,  though  it  was  many 
years  before  synthetical  methods  of  producing  organic  substances 
became  a  well-established  laboratory  procedure.  The  formation 
of  urea  from  ammonium  cyanate  evidently  involves  a  considerable 
rearrangement  within  the  molecule,  but  we  have  already  noted 
that  the  atoms  in  hydrocyanic  and  cyanic  acids  appear  to  be 
unusually  mobile  (p.  151).  The  reaction  is  not  a  complete  one, 
as  it  is  reversible. 

Other  ways  of  forming  urea  are:  2.  By  leading  a  mixture  of 
carbon  dioxide  and  ammonia  through  a  tube  heated  to  a  faint 
red,  cyanic  acid  being  an  intermediate  product.  3.  From  ammon- 
ium carbamate  at  i3o°-i4o°,  also  essentially  a  synthesis  from 
carbon  dioxide  and  ammonia.  4.  By  passing  carbonyl  sulphide, 
CO.S  (p.  242),  into  a  strong  solution  of  ammonia.  Ammonium 
thiocarbamate,  NH^.CO.SNHU,  is  first  formed  but  readily  breaks 
down  into  hydrogen  sulphide  and  urea,  especially  when  shaken 
with  lead  carbonate. 


232  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

1.  Like  other  acid  amides,  urea  is  hydrolyzed  when  its  solutions 
are  heated  with  acids  or  alkalies,  the  products  being  ammonia 
and  carbon  dioxide  (carbonic  acid) : 

CO(NH2)2  +  H2O  =  CO2  +  2NH3 

This  hydrolysis  occurs  in  urine  through  the  action  of  certain 
organisms,  so  that  the  urine  that  is  normally  acid  becomes 
alkaline,  and  smells  of  ammonia. 

2.  Urea,  like  other  amides,  forms  salts  with  strong  acids,  such 
as  the  nitrate,  whose  formula  has  been  given,  and  the  difficultly 
soluble   oxalate,  2CO.(NH2)2,(CO.OH)2,  only  one  of  the  amido 
groups  reacting  with  acids. 

3.  Nitrous  acid  acts  on  urea,  as  on  the  amides  and  primary 
amines,  with  the  production  of  nitrogen  and  carbonic  acid : 

CO(NH2)2  +  2HN02  =  2N2  +  C02  +  2H2O 

4.  A  solution  of  sodium  hydroxide  and  bromine  (in  which 
sodium  hypobromite  is  present)   effects  a  like  reaction   with 
formation  of  sodium  carbonate  and  nitrogen.    This  is  often  em- 
ployed for  the  determination  of  the  amount  of  urea  in  solution 
by  measurement  of  the  nitrogen,  but  in  the  case  of  urine  it  is  not 
a  very  exact  method: 

CO(NH2)2  +  3NaOBr  =  N2  +  3NaBr  +  CO2  +  2H2O 

A  test  for  urea  (also  given  by  proteins)  is  made  by  heating  the 
solid  substance  and  then  treating  it  with  a  solution  of  alkali  con- 
taining a  little  copper  sulphate.  A  reddish- violet  color  is  pro- 
duced. (Biuret  test.) 

5.  By  reaction  of  ammonia  with  carbonyl  chloride — a  general 
reaction  of  acid  chlorides.     If  instead  of  carbonyl  chloride,  di- 
phenyl  carbonate,  CO(OC6H5)2,  is  first  made  by  the  action  of 
the  sodium  salt  of  phenol  on  carbonyl  chloride,  and  this  is  then 
treated  with  ammonia,  the  reaction  is  especially  successful. 

6.  Cyanamide  (p.  149)  is  hydrolyzed  in  the  presence  of  a  little 
inorganic  acid  to  urea:     CN-NH2  +  H20  =  CO(NH2)2 


DERIVATIVES   OF  CARBONIC  ACID  233 

The  composition  of  urea  and  its  formation  from  carbonyl 
chloride  are  sufficient  evidence  for  the  structure  which  is  repre- 
sented by  its  formula. 

Properties  and  Reactions. — Urea  crystallizes  in  a  form  resembling 
that  of  saltpeter.  It  melts  at  13  2°  and  at  a  higher  temperature  de- 

/NHa 
composes  first  into  ammonia  and  biuret,  CO  ;  and 

\NH.CO.NH2 

gives  as  a  final  product  cyanuric  acid  (p.  149).  Urea  is  readily 
soluble  in  water  and  in  alcohol. 

Derivatives  of  Urea  and  Related  Substances. — Guanidine, 
HN:  C(NH2)2,  was  first  obtained  from  guanine,  a  purine  base  (see 
p.  235)  of  complicated  structure.  Guanidine  can  be  made  by 
heating  ammonium  thiocyanate  to  i8o°,or  by  heating  an  alcoholic 
solution  of  cyanamide  with  ammonium  chloride: 

/NH2.HC1 
CN.NH2  +  NH3.HC1  =  NH:C< 

XNH2 

It  is  a  crystalline  substance  of  strong  basic  properties,  which  is 
converted  into  urea  by  baryta  water. 

<V-/1 
>  or  urea  chloride  is  half  carbonyl 

chloride  and  half  amide.  It  can  be  made  by  leading  carbonyl 
chloride  over  heated  ammonium  chloride.  It  reacts  vigorously 
with  water  to  form  ammonium  chloride  and  carbon  dioxide;  with 
ammonia  or  amines  it  gives  urea  or  alkyl-substituted  ureas;  with 
alcohols  it  forms  amido-carbonic  or  carbamic  acid  esters: 


CO  +  C2H6OH  =  CO  +  HC1 

\NH2  \NH2 

These  esters  of  carbamic  acid  are  called  urethanes. 


234  INTRODUCTION  TO  ORGANIC   CHEMISTRY 

Alkyl  derivatives  of  urea,  in  which  the  hydrogen  is  partly  or 
wholly  replaced  by  alkyl  groups,  are  known  in  large  number, 

Uric  acid,  C5H4O3N4,  is  a  white,  crystalline  substance,  without 
odor  or  taste.  It  is  present  in  small  amount  in  normal  human 
urine,  and  occurs  in  large  quantities  in  the  excrement  of  birds 
(guano)  and  of  reptiles  in  the  form  of  ammonium  urate.  It  is 
conveniently  prepared  from  these  Jatter  sources.  Uric  acid  is 
almost  insoluble  in  water.  It  is  a  feeble  dibasic  acid  (though 
containing  no  carboxyl  group).  Its  alkali  salts  are  sparingly 
soluble,  the  lithium  salt  dissolving  more  freely  than  the  others. 

When  heated  with  acids  uric  acid  gives  glycocoll  (p.  254), 
ammonia,  and  carbon  dioxide.  On  oxidation  with  cold  nitric  acid 
there  are  formed  urea  and  alloxan, 

NH— CO 

I          I 
CO     CO 

I     I 

NH— CO 

and  with  alkaline  permanganate  the  product  is  allantoin  whose 
formula  has  been  shown  to  be 

NH.CH.NH.CO.NH2 

CO 

\ 

NH.CO 

On  the  basis  of  these  reactions  Medicus  proposed  a  formula  for 
uric  acid  which  was  long  in  dispute  but  after  many  years  of 
investigation  by  E.  Fischer  and  others  was  confirmed  by  success- 
ful syntheses.     This  formula  is: 
NH  -  CO 

I  I 

CO       C— NH 

I        II      >co 

NH  -  C— NH 


DERIVATIVES   OF   CARBONIC   ACID  23$ 

A  reaction  of  the  acid  with  phosphorus  oxychloride  by  which 
the  three  oxygen  atoms  and  three  hydrogen  atoms  are  replaced 
by  three  chlorine  atoms  suggests  an  enol  tautomeric  structure: 

N=COH 

I        I 
HOC     C  -  NH 

||  >  COH 

N — C  -  N 

Uric  acid  and  a  number  of  other  important  natural  products 
such  as  caffeine,  theobromine,  xanthine  and  guanine  all  contain 
the  same  carbon  and  nitrogen  skeleton  in  their  structural  formu- 
las, and  may  be  regarded  as  derivatives  of  a  hydrogen  compound 
which  Fischer  called  purine  (from  purum  and  uricum)  and  suc- 
ceeded in  preparing  in  1898. 

Purine  Bases. — Guanine  occurs  in  animal  tissues  and  in  guano, 
and  in  the  form  of  a  calcium  salt  in  fish  scales.  It  is  a  colorless 
powder  very  slightly  soluble  in  water,  and  combines  with  both 
acids  and  bases.  On  oxidation  it  gives  guanidine  (p.  233)  and 
parabanic  acid  which  hydrolyzes  into  urea  and  oxalic  acid.  Heated 
with  hydrochloric  acid  it  decomposes  into  glycocoll,  formic  acid, 
ammonia,  and  carbon  dioxide.  By  nitrous  acid  it  is  converted 
into  xanthine. 

Xanthine  is  found  in  all  tissues  of  the  body.  It  unites  with 
both  acids  and  bases.  When  oxidized  it  yields  alloxan  and  urea. 
Theobromine  is  formed  by  the  reaction  of  its  lead  salt  with 
methyl  iodide. 

Theobromine  occurs  in  cocao,  beans.  It  is  a  white  crystalline 
powder,  and  is  amphoteric  in  its  behavior.  Its  oxidation  prod- 
ucts are  methyl  alloxan  and  methyl  urea.  Its  silver  salt  with 
methyl  iodide  gives  caffeine. 

Caffeine  or  theme  is  a  ingredient  of  coffee  and  tea  and  occurs  in 
the  cola  nuts,  etc.  It  crystallizes  with  one  molecule  of  water  in 
silky  needles,  and  is  weakly  basic.  It  can  be  oxidized  into  dimeth- 


23  5* 


INTRODUCTION   TO    ORGANIC   CHEMISTRY 


ylalloxan  and  monomethylurea.  When  decomposed  by  hydro- 
chloric acid,  its  nitrogen  appears  partly  as  ammonia  and  partly 
as  methylamine. 


N=  CH 

CH     C  -  NH 

II          II        >CH 

N  — C-N 

Purine 

N(CH3)— CO 

CO  C  -  N(CH3) 

I  II        >CH 

N(CH3)— C  -  N 


N 


Caffeine 

COH 


C  -  NH2  C  -  NH 


N 


C-N 

Guanine 


CO 


NH- 

I  I 

CO  C  -  N(CH3) 

I  II         >CH 

N(CH3)  —C-N 

Theobromine 

NH— CO 

I  I 

CO      C  -  NH 

I  II        >CH 

NH  -  C  -  N 

Xanthine 


CHAPTER  XVII 
COMPOUNDS  CONTAINING  SULPHUR 

Sulphur  is  found  in  only  a  few  natural  organic  compounds  of 
established  chemical  constitution,  as  for  instance  in  the  mustard 
oils  (p.  153);  but  it  is  usually  present  in  the  protein  substances 
which  are  essential  constituents  of  all  living  cells,  and  of  whose 
chemical  structure  comparatively  little  is  yet  known.  Many 
organic  compounds  containing  sulphur  have,  however,  been  made 
by  laboratory  methods.  Some  of  these  in  which  sulphur  is  linked 
to  carbon  by  oxygen,  such  as  the  alkyl  sulphates,  have  already 
been  described.  We  have  also  noticed  a  few  others  where  carbon 
and  sulphur  are  directly  united,  as  in  thio  and  isothiocyanic 
acids  and  their  esters. 

In  inorganic  chemistry  we  have  learned  that  sulphur  and 
oxygen  form  many  similar  compounds,  the  sulphides  and  hydro- 
sulphides  generally  having  formulas  which  find  their  analogies  in 
those  of  the  oxides  and  hydroxides.  The  same  is  true  in  organic 
chemistry;  and  sulphur  alcohols,  esters,  aldehydes,  ketones,  and 
acids  can  be  readily  made  in  which  sulphur  takes  the  place  of 
oxygen  in  the  ordinary  compounds  of  these  names.  In  all  these 
substances  sulphur  is,  like  oxygen,  divalent.  But  sulphur  in  in- 
organic compounds  is  also,  on  occasion,  tetravalent  or  hexavalent, 
these  higher  valencies  appearing  especially  in  compounds  in  which 
it  is  combined  wholly  or  partly  with  oxygen,  as  in  its  oxides  and 
acids.  Similarly,  in  organic  chemistry,  tetravalent  or  hexavalent 
sulphur  appears,  often  as  a  linking  element  between  oxygen 
and  alkyl  groups.  Sulphur  atoms  also  show  a  tendency  to  link 
with  each  other  as  oxygen  seldom  does.  Consequently,  there 

236 


237  COMPOUNDS  CONTAINING   SULPHUR 

are  many  thio-organic  compounds  which  find  no  analogies  among 
those  of  oxygen. 

Almost  all  of  the  organic  sulphur  compounds  are  laboratory 
products,  as  already  indicated.  Those  which  are  of  the  type  of 
oxygen  compounds  are  made  by  analogous  methods.  They 
are,  in  general,  less  stable  than  the  corresponding  oxygen  com- 
pounds, which  accords  with  our  knowledge  of  the  inorganic  sulphur 
compounds;  and  those  which  are  volatile  are  characterized  by 
most  objectionable  odors. 

When  alcohols  and  ethers  are  oxidized,  the  hydrogen  of  the 
alkyl  groups  is  at  once  affected  with  the  production  of  aldehydes, 
acids,  and  ketones.  The  corresponding  sulphur  compounds,  on 
the  other  hand,  give  a  series  of  oxidation  products  in  which  the 
hydrogen  combined  with  sulphur  may  be  removed,  or  oxygen 
added  to  the  sulphur. 

The  thioalcohols,  CnH2n  +  i.SH,  give  as  their  first  oxidation 
product  disulphides,  CnH2n  +  i.S  —  S.CnH2n  +  i.  On  more  ener- 
getic oxidation,  the  valence  of  the  sulphur  is  increased,  and  sul- 
phonic  acids  are  formed,  whose  formula  is  probably, 

CH       s4 

+     \OH 

In  like  manner,  the  thioethers,  (CnH2n  +  i)2S,  are  oxidized  first 
to  sulphoxides  (CnH2n  +  i)2S  =  O,  in  which  sulphur  is  tetra- 

valent,    and   then    to    sulphones,    (CnH2n  +  i)2S^  ,  where  the 


valence  has  become  six.1 

The  disposition  of  sulphur  to  change  from  divalency  to  a  higher 
valence  is  also  shown  by  the  formation  of  addition  compounds. 

1  The  structure  of  the  sulphur  oxygen  groups  in  the  sulphonic  acids  and 
sulphones  is  not  entirely  certain.  It  may  be  =  S  \tt  in  which  case  sulphur  is 
tetravalent. 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  238 

The  alkyl  sulphides  unite  with  alkyl  halides  forming  such  com- 
pounds as  (CnH2n+l)3SI. 

Thioalcohols  are  prepared  by  the  action  of  alcoholic  potassium 
hydrosulphide  on  alkyl  halides  or  potassium  alkyl  sulphates: 

C2H5C1  +  KSH  =  C2H5SH  +  KC1 
C2H6O.SO2.OK  +  KSH  =  C2H6SH  +  K2SO4 

These  reactions  are  exactly  analogous  to  those  for  making 
alcohols.  The  first  is  carried  out  by  heating  under  pressure,  the 
second  takes  place  on  distillation. 

The  thioalcohols  are  volatile  liquids  whose  boiling  points  are 
much  lower  than  those  of  the  corresponding  alcohols  (methyl 
thioalcohol  boils  at  6°).  They  are  almost  insoluble  in  water,  but 
dissolve  easily  in  alcohol  and  in  ether.  The  products  of  their 
oxidation  have  already  been  given.  As  in  the  case  of  the  alcohols, 
the  hydrogen  of  the  SH-group  can  be  replaced  by  metals,  with  the 
formation  of  salt-like  compounds.  But  these  compounds  are 
more  stable  than  the  alcoholates,  and  are  formed  with  heavy 
metals  such  as  lead,  copper,  and  mercury.  With  mercuric  oxide, 
for  instance,  thioethyl  alcohol  readily  forms  (C2H5S)2Hg,  which 
can  be  crystallized  from  alcohol.  On  account  of  the  formation 
of  these  mercury  compounds,  the  thioalcohols  were  called  mer- 
captans  (corpus  mercuiio  aptum),  a  name  which  is  still  commonly 
used,  and  the  salts  are  called  mercaptides. 

The  odor  of  ethyl  mercaptan  is  not  only  very  disagreeable  but 
so  intense  that  it  is  said  that  0.000,000,002  mg.  can  be  detected, 
an  amount  about  250  times  less  than  that  of  sodium  which  can 
be  recognized  by  the  spectroscope. 

Ethyl  mercaptan  is  made  commercially,  and  used  in  the 
preparation  of  sulphonal  (p.  240). 

Thioethers  may  be  made  in  a  manner  analogous  to  that  for 
making  ethers,  by  the  reaction  of  alkyl  halides,  or  alkali  alkyl 
sulphates  with  sodium  mercaptides: 

C2H6O.S02.OK  +  CH3SK  =  C2H6.S.CH3  +  K2SO4 


239  COMPOUNDS    CONTAINING   SULPHUR 

Both  simple  and  mixed  thioethers  may  be  thus  prepared.  The 
thioethers  are  also  made  by  the  action  of  potassium  sulphide 
on  the  above  alkyl  compounds: 

2C2H5I  +  K2S  =  (C2H5)2S  +  2KI 

The.  analogous  reaction  with  the  alkali  oxide  does  not  take  place, 
but  can  be  carried  out  with  dry  silver  oxide  and  alkyl  halide. 

The  thioethers  are  liquids  insoluble  in  water,  and  having 
higher  boiling  points  than  the  corresponding  mercaptans. 
(Compare  this  with  the  boiling  points  of  alcohols  and  ethers.) 
As  has  already  been  stated,  they  are  readily  oxidized.  They  form 
addition  products  not  only  with  alkyl  halides,  but  also  combine 
with  halogen  salts  of  metals,  and  with  bromine  and  iodine,  with  the 
production  of  crystalline  compounds. 

Sulphonium  Bases  and  Salts. — The  addition  products  which 
the  thioethers  or  alkyl  sulphides  form  with  alkyl  halides,  such  as 
(C2H5)3SI,  are  salt-like  compounds,  from  whose  aqueous  solutions 
other  salts  may  be  made  by  reaction  with  silver  salts: 

(CH3)3SI  +  AgN03  =  (CH3)3SN03  +  Agl 

By  the  action  of  silver  hydroxide,  strongly  alkaline  solutions 
are  obtained,  which  yield  on  evaporation  deliquescent  crystals 
of  sulphonium  hydroxide: 

.       (CH3)3SI  +  AgOH  =  (CH3)3SOH  +  Agl 

The  sulphonium  hydroxide  solutions  are  strongly  basic  and 
precipitate  hydroxides  of  metals,  set  ammonia  free  from  its  salts, 
and  absorb  carbon  dioxide  from  the  air,  as  do  the  hydroxides  of 
potassium  and  sodium. 

In  the  manner  of  their  formation  and  their  behavior  they  are 
analogous  to  the  tetra-alkyl  ammonium  bases  (p.  135).  On  heat- 
ing, the  sulphonium  halides  decompose  into  the  alkyl  sulphides 


INTRODUCTION  TO   ORGANIC   CHEMISTRY  240 

and  alkyl  halides,  reversing  the  reaction  by  which  they  are  formed, 
and  behaving  in  this  respect  like  %the  tetra-alkyl  ammonium 
salts. 

Bisulphides,  such  as  C2H5.S  —  S.C2H6,  are  formed  by  careful 
oxidation  (often  through  oxidation  in  the  air)  of  the  mercaptans. 
They  are  also  formed  by  distilling  potassium  ethyl  sulphate  with 
potassium  disulphide;  and  when  mercaptans  are  treated  with 
concentrated  sulphuric  acid,  the  product  is  not  the  thioether 
(analogous  to  ordinary  ether  formation)  but  the  disulphide. 

The  disulphides  are  liquids  which  boil  higher  than  the  corre- 
sponding sulphides.  They  are  easily  reduced  to  mercaptans. 

Thioacids,  in  which  the  SH-group  appears  in  place  of  the 
hydroxyl  group,  can  be  made  by  heating  oxygen  acids  with  phos- 
phorus pentasulphide,  or  through  the  action  of  potassium 
hydrosulphide  on  the  acid  chlorides.  The  thioacids  have  lower 
boiling  points  and  are  less  soluble  than  the  corresponding  oxygen 
acids.  Their  salts  with  the  heavy  metals  are  mostly  difficultly 
soluble  and  are  easily  decomposed  with  the  formation  of  metal 
sulphides. 

Thioaldehydes,  and  thioketones  are  formed  when  hydrogen 
sulphide  is  passed  into  solutions  of  aldehydes  or  ketones  to  which 
hydrochloric  acid  is  added;  but  these  compounds  polymerize  so 
readily  (the  ketones  as  well  as  the  aldehydes)  that  the  monomo- 
lecular  substances  have  not  been  prepared  in  the  pure  state. 

Alkyl  sulphoxides,  such  as  C2H5.SO.C2H5,  are  the  first  product 
of  oxidation  of  the  thioethers  by  nitric  acid.  They  cannot 
be  distilled  without  decomposition,  and  are  readily  reduced  to 
thioethers  again. 

Sulphones,  of  the  type  of  C2HB.SO2.C2HB,  are  formed  by 
vigorous  oxidation  of  thioethers  or  the  alkyl  sulphoxides.  They 
are  not  reduced  by  nascent  hydrogen. 

Sulphonal,  which  is  employed  in  medicine  as  a  soporific,  is  a 
disulphone,  (CH3)2C(SO2.C2H5)2,  diethyl-sulphon-dimethyl 
methane.  It  is  made  by  "  condensation "  of  acetone  and  ethyl 


241  COMPOUNDS   CONTAINING   SULPHUR 

mercaptan   through   the   influence   of   hydrochloric   acid,    and 
oxidation  of  the  product: 


CH3.CO.CH3  +  2C2H5SH  =  (CH3)2C.(SC2H6)2  +  H2O 

Acetone 

(CH3)2C(SC2H5)2  +  40  =  (CH3)2C.(S02.C2H5)2 

Sulphonal 

Other  analogous  compounds  are  made  in  a  similar  manner. 

Sulphonic  acids  are  compounds  in  which  one  hydroxyl  group 
in  sulphuric  acid  is  replaced  by  a  hydrocarbon  radical.  They 
are  formed  by  vigorous  oxidation  of  mercaptans  by  nitric  acid, 
and  their  salts  can  be  made  by  the  action  of  alkyl  iodides  on  an 
alkali  sulphite: 

C2H5I  +  KSO3K  =  C2H5.SO3K  +  KI 

By  phosphorus  pentachloride  the  sulphonic  acids  are  converted 
into  acid  chlorides,  e.g.,  C2H5.SO2.C1,  and  these  are  reduced  to 
mercaptans  by  nascent  hydrogen.  This  fact  together  with 
the  formation  of  the  sulphonic  acids  by  oxidation  of  mercaptans, 
indicates  that  in  them,  as  in  the  mercaptans,  sulphur  is  directly 
united  to  carbon.  Their  structure1  is,  therefore,  probably 


H 

The  sulphonic  acids  are  stable,  strongly  acid  compounds  which 
are  very  soluble  in  water  and  give  deliquescent  crystals.  They 
form  alkali  salts  with  solutions  of  caustic  alkalies,  but  are  other- 
wise unaffected,  even  on  boiling,  and  they  are  not  acted  on  by 
boiling  acids.  When  melted  with  solid  alkalies,  however,  they 
are  decomposed  with  the  formation  of  alcohols  and  alkali  sulphites : 

C2H5.SO2OH  +  2KOH  =  C2H5OH  +  K2S03  +  H2O 

1  This  conclusion  as  to  the  structure  of  the  sulphonic  acids,  and  the  fact 
that  they  can  be  made  by  the  reaction  of  alkali  sulphites  and  alkyl  iodide, 
indicates  that  the  structure  of  the  sulphites  is  KSO2 .  OK,  rather  than  KO .  SO. 
OK,  and  that  a  similar  constitution  should  be  assigned  to  the  unstable  sul- 
phurous acid. 


INTRODUCTION  TO   ORGANIC   CHEMISTRY  242 

Esters  of  sulphonic  acids,  such  as  C2H5.SO2.O.CH3  are  made  by 
the  usual  methods  of  ester  formation.  The  aliphatic  sulphonic 
acids  are  of  comparatively  little  importance;  but  the  sulphonic 
acids  of  the  aromatic  compounds  are  extensively  employed  in 
synthetical  operations  both  in  the  laboratory  and  in  chemical 
manufactures. 

Sulphur  Compounds  Related  to  Carbonic  Acid 

Carbon  disulphide,  CS2,  is  the  analogue  of  carbon  dioxide,  and, 
like  it,  is  made  by  the  direct  union  of  the  elements,  when  sulphur 
vapor  is  passed  over  red-hot  carbon.  It  is,  however,  an  endother- 
mic  compond,  absorbing  about  twenty-five  large  calories  in  the 
formation  of  the  gram-molecular  weight,  while  the  formation 
of  the  gram-molecular  weight  of  carbon  dioxide  is  attended  with 
the  production  of  about  ninety-six  calories.  Carbon  disulphide 
is  a  strong  refracting  liquid,  which  boils  at  46°,  and  which  usually 
has  a  very  disagreeable  odor,  due  to  slight  impurities.  It  is  an 
excellent  solvent  for  phosphorus,  iodine,  oils,  fats,  and  rubber, 
and  is  largely  used. 

Carbon  oxysulphide,  CO.S,  is  formed  when  a  mixture  of  carbon 
monoxide  and  sulphur  vapor  is  passed  through  a  tube  heated  to  a 
faint  red  heat.  It  is  also  produced  by  the  action  of  hydrogen 
sulphide  on  isocyanic  esters: 

2C2H5NCO  +  H2S  =  CO.S  +  (C2H5.NH)2CO 

Ethyl  isocyanate  Substituted  urea 

It  may  also  be  prepared  by  the  action  of  strong  sulphuric  acid  on 
ammonium  or  potassium  thiocyanate: 

HSCN  +  H2O  =  CO.S  +  NH3 

Carbon  oxysulphide  is  an  inflammable  gas  of  faint  peculiar  odor. 
It  is  decomposed  by  alkalies  as  follows: 

CO.S  +  4KOH  =  K2CO3  +  K2S  +  2H2O 


243  COMPOUNDS   CONTAINING   SULPHUR 

Sulphur  Derivatives  of  Carbonic  Acid.  —  By  the  replacement 
of  oxygen  in  carbonic  acid  it  is  easily  seen  that  five  different 
sulphur  acids  might  be  formed.  The  acids,  themselves,  like 
carbonic  acid,  are  very  unstable,  and  with  one  exception,  CS(SH)2, 
are  not  known  in  the  free  state;  but  fairly  stable  neutral  or  acid 
esters,  and  salts  of  all  of  the  acid  esters  have  been  prepared. 

/SH 

Salts  of   the  acid  esters  of  thiocarbonic  acid.  CO\         ,  for  in- 

NDH 

stance,  may  be  prepared  by  leading  carbon  oxysulphide  into 
alcoholic  solutions  of  the  alkalies,  or  by  the  action  of  carbon 
dioxide  on  mercap  tides: 

/SK 
CO.S  +  C2H5OK  =  CO< 

XOC2H5 

/SK 

CO2  +  C2H5SK  =  C0<  ; 

XOC2H6 

/SH 

and   the    neutral   esters    of   the   dithiocarbonic    acid,  CO<T         , 

\SH 

are  made  by  the  reaction  of  alkali  mercaptides  with  carbonyl 
chloride. 
The  more  important  derivatives  of  these  acids  are  the  alkali 

/SH 
salts  of  the  acid  esters  of  sulphothiocarbonic  acid,  CS<T 

When  carbon  disulphide  is  shaken  with  a  strong  alcoholic  solu- 
tion of  potassium  hydroxide,  yellowish  silky  crystals  of  the  acid 
ethyl  ester  salts  are  precipitated.  The  crystals  are  readily 
soluble  in  water,  and  on  adding  dilute  sulphuric  acid  to  the  cold 


< 
,  separates  as  a  colorless 

oil.     Acids  of  this  type  are  called  xanthic  acids  and  their  salts 
xanthates    (£ap66*\  from    the    yellow    precipitate    of   cuprous 


% 

INTRODUCTION   TO   ORGANIC   CHEMISTRY  244 

xanthate  which  their  solutions  give  with  solutions  of  copper  salts. 
Traces  of  carbon  disulphide  can  be  detected  by  these  reactions. 

By  treatment  of  the  alkali  xanthates  with  alkyl  halides,  neutral 
esters  of  xanthic  acid  are  formed. 

Thiourea,  CS(NH2)2,  is  formed  from  ammonium  thiocyanate 
as  urea  is  from  the  cyanate.  It  is  necessary,  however,  to  melt  the 
solid  salt,  as  the  transformation  does  not  occur  on  simple  evapora- 
tion of  the  solution  as  in  the  case  of  the  cyanate.  It  is  also  a 
reversible  reaction  and  remains  incomplete.  Thiourea  is  con- 
verted into  urea  by  adding  to  its  cold  solution  potassium  perman- 
ganate as  long  as  this  is  decolorized.  Mercuric  oxide  added  to 
solutions  of  thiourea  gives  cyanamide,  mercuric  sulphide  and 
water. 


CHAPTER  XVIII 

SOME  HALOGEN  AND  AMINO  DERIVATIVES 
Halogen  Derivatives 

Halogen-substituted  Alcohols. — When  chlorine  (or  bromine) 
acts  on  an  alcohol  its  attack  is  first  directed  to  the  group  con- 
taining hydroyxl  with  the  formation  of  a  carbonyl  group.  Prob- 
ably the  replacement  of  a  hydrogen  atom  of  the  alcohol  group 
occurs  first  and  the  group  thus  formed,  with  halogen  and  hy- 
droxyl  united  to  the  same  carbon  atom,  is  too  unstable  to  exist, 
so  that,  as  in  most  cases  of  corresponding  dihydroxyl  compounds, 
it  at  once  breaks  down. 

Thus  the  action  results  in  an  indirect  oxidation  with  the  pro- 
duction of  the  aldehyde  group  in  the  case  of  a  primary  alcohol: 


CH3.CH2OH  -»  CH3.CH<         -»  CH3.CHO  +  HC1 
XC1 

and  of  the  ketone  group  with  a  secondary  alcohol: 

/OH 
CH3  CHOH.CH3  -»  (CH3)2C<        ->  CH3.CO.CH3  +  HC1 


Further  action  of  chlorine  causes  replacement  of  hydrogen  in  the 
associated  alkyl  group  or  groups.  Therefore,  the  product  actually 
obtained  is  a  chloraldehyde  (cf.  chloral,  p.  91),  from  a  primary 
alcohol,  or  a  chloracetone,  if  a  secondary  alcohol  is  used. 

Although  chloralcohols  with  chlorine  and  hydroxyl  united  to 
the  same  carbon  atom  do  not  exist,  the  corresponding  esters  in 
which  the  hydroxyl  hydrogen  is  replaced  by  an  alkyl  group  are 

245 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  246 

comparatively  stable.  Thus  by  the  action  of  chlorine  on  ethyl 
ether  (kept  cool  and  in  the  dark  to  avoid  explosive  action),  there 
may  be  obtained  as  the  first  product, 


CH3.CH 

xa 

Substances  of  this  type  are  called  chlorethers.  The  constitution 
indicated  by  the  formula  is  proved  by  the  products  of  hydrolysis 
with  sulphuric  acid  as  a  catalytic  agent,  viz.,  alcohol,  aldehyde, 
and  hydrogen  chloride: 

/OC2H5 
CH3.CH<  +  H2O  -*  C2H5OH  + 


(CH3.CH  ->  CHaCHO  +  HC1 


Halogenhydrins.  —  Halogen-substituted  alcohols  in  which  the 
halogen  and  hydroxyl  are  united  to  different  carbon  atoms  can  be 
obtained  indirectly  in  several  ways.  They  are  called  halogen- 
hydrins.  Chlorhydrins  are  formed: 

1.  By  the  action  of  hydrogen  chloride  on  glycols: 

CH2OH.CH2OH  +  HC1  =  CH2C1.CH2OH  +  H2O 

2.  From  defines  by  addition  of  hypochlorous  acid  (p.  47): 

CH2:CH2  +  HC1O  =  CH2C1.CH2OH 

From  alkylene  oxides  (which  are  themselves,  however,  prepared 
from  the  chlorhydrins  p.  157),  by  addition  of  hydrogen  chloride: 

CH2\  CH2C1 

|      >0  +  HC1  =   | 
CH/  CH2OH 


247  SOME   HALOGEN  AND  AMINO   DERIVATIVES 

The  bromhydrins  are  made  by  the  same  methods,  but  the  meth- 
ods are  not  effective  for  iodohydrins.  These  may  be  prepared  by 
the  action  of  potassium  iodide  on  the  chlorhydrins: 

CH2.C1.CH2OH.+  KI  =  CH2LCH2OH  +  KC1 

Properties  and  Reactions. — The  halogenhydrins  have  the  prop- 
erties and  give  the  reactions  of  both  alkyl  halides  and  alcohols. 
Since  they  can  be  made  directly  from  the  polyhydroxyl  alcohols, 
they  serve  as  a  means  for  passing  from  one  such  alcohol  to  others 
with  fewer  hydroxyl  groups.  Both  the  hydroxyl  group  and  the 
halogen  are  affected  when  a  halogenhydrin  is  treated  with  alkalies, 
and  alkylene  oxides  are  formed: 

CH2V 

CH2C1.CH2OH  +  KOH  =   |       >O  +  KC1  +  H2O 

CH/ 

Of  the  halogen-substituted  aldehydes,  chloral,  CC13.CHO, 
is  the  most  important  representative  (cf.  p.  91).  The  formation 
of  halogen  ketones  and  ethers  has  already  been  alluded  to.  The 
chlor  and  brom-ketones  as  well  as  the  ethers  may  be  made  by 
direct  action  of  the  halogen. 

Halogen-substituted  Acids. — Chlorine  and  bromine  do  not  act 
very  readily  on  the  saturated  acids,  but  the  action  is  assisted  by 
sunlight,  or  by  the  presence  of  a  catalytic  agent,  such  as  iodine  or 
sulphur.  The  substitution  takes  place  much  more  rapidly  in  the 
acid  chlorides  or  bromides,  or  the  acid  anhydride,  and  is  more 
easily  effected  the  higher  the  molecular  weight  of  the  acid.  Since 
the  substituted  acid  halides  or  anhydrides  are  readily  converted 
into  the  corresponding  acids,  they  are  usually  employed  in  making 
the  chlor  and  brom-acids.  Iodine  is  usually  introduced  by  reac- 
tion of  the  chlor-acids  with  potassium  iodide.  Direct  chlorina- 
tion  or  bromination  gives  generally  a-substitution  products,  or 
products  in  which  the  halogen  is  united  to  the  car-bon  atom 
standing  next  to  the  carboxyl  group. 

/3-,  7,-  and  6-compounds  are  usually  formed  by  the  addition  of 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  248 

the  hydrogen  halide  to  unsaturated  acids,  the  halogen  in  this 
case  usually  entering  at  a  point  as  far  removed  from  the  carboxyl 
group  as  possible : 
CH3.CH:CH.CH2.CO.OH.  +  HBr  = 

Ethylidene-propionic  acid 

CH3.CHBr.CH2.CH2.CO.OH 

•y-brompropylacetic  acid 

CH2 :  CH.CH2.CH2.CO.OH  +  HBr  = 

Ally  lace  tic  acid 

CH2Br.CH2.CH2.CH2.CO.OH 

5-brompropylacetic  acid 

More  than  one  atom  of  chlorine  or  bromine  can  be  substituted 
by  further  direct  action  of  the  halogen  on  the  monosubstituted 
acid.  Chlorine  is  allowed  to  act  in  solution  in  carbon  tetra- 
chloride  when  possible,  while  bromine  often  acts  without  a  solvent. 

It  is  also  possible  to  obtain  the  halogen-substituted  acids  by 
introduction  of  the  carboxyl  group  into  other  halogen-substituted 
compounds  or  by  oxidation  'of  the  substituted  alcohols  or  alde- 
hydes. Thus  trichloracetic  acid  is  prepared  by  oxidizing  chloral 
by  means  of  nitric  acid : 

CC13.CHO  +  O  =  CC13.CO.OH 

Other  methods  for  introducing  the  carboxyl  group  may  be 
employed  as,  for  instance,  through  the  cyanogen  group. 

Chlorformic  add,  Cl.CO.OH,  can  exist  only  in  the  form  of 
its  esters. 

Chloracetic  Acids. — Monochloracetic  acid,  CH2C1.CO.OH,  may 
be  prepared  by  the  direct  action  of  chlorine  on  boiling  acetic 
acid  to  which  some  sulphur  has  been  added.  It  forms  crystals 
which  melt  at  63°.  It  is  a  stronger  acid  than  acetic  acid.  Di- 
Mor acetic  acid,  CHC12.CO.OH,  can  be  made  by  further  action  of 
chlorine  on  acetic  acid  or  on  the  monochloracid,  but,  as  this 
gives  a  mixture  of  chloracetic  acids,  it  is  best  prepared  by  boiling 
chloral  hydrate  with  a  solution  of  potassium  cyanide.  The  reac- 
tion occasions  a  rearrangement  which  is  rather  unusual: 

CC13.CH(OH)2  +  KCN  =  CHC12.CO.OH  +  HCN  +  KC1 


249  SOME  HALOGEN  AND  AMINO  DERIVATIVES 

This  acid  is  liquid  at  ordinary  temperatures,  having  a  melting 
point  of  —4°.  Trichloracetic  acid  is  made  by  the  oxidation  of 
chloral,  as  given  above.  It  is  a  solid,  melting  at  55°.  Though  it 
stands  so  near  to  chloral  in  its  structure,  it  has  no  trace  of  the 
physiological  effect  of  this  substance. 

The  discovery  of  trichloracetic  acid  by  Dumas  in  1839  had  a 
very  important  influence  on  chemical  theory,  the  fact  that  the 
strongly  negative  element  chlorine  could  be  substituted  for 
hydrogen  without  changing  the  essential  nature  of  the  compound 
leading  to  the  overthrow  of  the  dualistic  theory  of  Berzelius. 

Trichloracetic  acid  has  also  a  further  historical  interest 
through  the  demonstration  in  1845  by  Kolbe  of  a  method  of  its 
synthesis  from  the  elements.  As  the  reduction  of  the  trichlor- 
acetic acid  to  acetic  acid  by  potassium  amalgam  in  aqueous  solu- 
tion had  already  been  effected,  the  synthesis  of  acetic  acid  from 
its  elements  for  the  first  time  was  accomplished.  Kolbe's  syn- 
thesis was  as  follows: 

Q.  Heat   CC12  C12,H20  CO.OH 

C  +  28  -»  CS2 >CC14 »  ||  > 

CC12         Sunlight         CC13 

The  chloracetic  acids  are  all  soluble  in  water.  The  mono- 
chloracetic  acid  is  decomposed  by  boiling  its  solutions,  with  the 
production  of  glycollic  acid,  CH2OH. CO.OH.  Dichloracetic 
acid  in  solution  is  decomposed  slowly  at  100°,  more  rapidly  when 
heated  in  a  sealed  tube  to  higher  temperatures,  and  yields  gly- 
oxylic  acid,  CHO.CO.OH.  Trichloracetic  acid  is  more  unstable, 
and  on  boiling  its  solution  gives  chloroform  and  carbon  dioxide: 

CC13.CO.OH  =  CHC13  +  CO2 

These  reactions  are  effected  more  rapidly  by  alkalies  or  silver 
hydroxide. 

General  Properties  of  the  Halogen-substituted  Acids. — The 
substitution  of  halogen  atoms  for  hydrogen  increases  the  acid 
character;  the  influence  of  chlorine  being  greater  than  that  of 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  250 

bromine,  and  that  of  bromine  greater  than  that  of  iodine.  The 
position  of  the  substituted  halogen  also  has  an  influence  on  the 
acidity;  being  less  effective  the  further  it  is  removed  from  the 
carboxyl  group.  The  activity  of  acids  is  measured  by  their  dis- 
sociation-constants, and  from  determinations  of  these  it  appears 
that  the  strength  of  monochloracetic  acid  is  about  eighty-six 
times  that  of  acetic  acid.  Introduction  of  a  second  chlorine  atom 
multiplies  this  strength  by  33,  and  trichloracetic  acid  is  about 
23 . 5  times  as  strong  as  the  dichlor-acid,  or  nearly  67,000  times  as 
strong  an  acid  as  acetic  acid. 

While  the  presence  of  the  halogen  thus  influences  the  acid 
character,  the  carboxyl  group  has  a  reciprocal  influence  on  the 
stability  of  the  halogen.  In  the  alkyl  halides  the  hatogen  can  be 
replaced  by  hydroxyl,  or  an  unsaturated  hydrocarbon  produced, 
by  means  of  alkali  hydroxides,  but  the  reaction  is  slow,  and  usu- 
ally requires  heating  to  a  high  temperature  (in  sealed  tubes)  for 
hours.  With  the  halogen-substituted  acids,  however,  the  same 
reaction  takes  place  much  more  readily.  The  influence  of  the 
carboxyl  group  on  the  reactivity  of  the  halogen,  like  that  of  the 
halogen  on  the  acidity,  depends  upon  the  relative  position  of  the 
halogen  and  carboxyl  in  the  molecule.  With  a-compounds,  there 
is  substitution  of  hydroxyl  for  the  halogen;  with  /3-compounds  and 
alcoholic  solutions  of  alkalies  the  chief  product  is  an  unsaturated 
acid;  with  y-compounds,  the  hydroxyl  acids  which  are  first  formed 
break  down  easily  into  lactones  (p.  172). 

The  j8-halogen-substituted  acids  enter  into  a  characteristic 
reaction  with  sodium  carbonate  by  which  the  sodium  salt  which 
is  first  formed  is  decomposed  with  the  formation  of  an  unsaturated 
hydrocarbon : 

Na2COs 

CH3.CHBr.CH(CH3).CO.ONa >CH3.CH:CH.CH3 

/3-brommethylethyl  acetic  acid  Butylene 

+  NaBr  +  CO2 

By  means  of  potassium  cyanide,  the  halogen  in  all  monohalogen 
acids  is  replaced  by  cyanogen  and  the  compound  thus  becomes 


251  SOME  HALOGEN  AND   AMINO   DERIVATIVES 

the  half-nitrile  of  a  dibasic  acid.  Hence  the  monohalogen  acids 
are  a  means  for  building  up  dicarboxylic  acids  from  monocarboxy- 
lic  acids. 

Ammonia  reacts  with  the  monohalogen  acids  with  the  produc- 
tion of  amino-acids. 

Ammo -compounds 

Ammo-alcohols. — We  have  already  met  with  compounds  in 
which  the  amino-group  and  hydroxyl  are  united  to  the  same 
carbon  atom — the  aldehyde-ammonias. 

Amino-alcohols  or  hydramines  in  which  hydroxyl  and  the  amino 
group  are  combined  with  different  carbon  atoms  of  a  hydrocarbon 
radical  can  be  made  by  the  action  of  ammonia  on  halogen  hydrins 
or  alkylene  oxides: 

CH2OH.CH2C1  +  NH3  =  CH2OH.CH2NH2  +  HC1 

CH2V 

|       >O  +  NH3  =  CH2OH.CH2NH2 
CH/ 

These  reactions  may  give  secondary  and  tertiary  derivatives, 
e.g.,  (CH2OH.CH2)2NH  and  (CH2OH.CH2)3N,  as  in  the  forma- 
tion of  amines  (p.  128). 

The  amino-alcohols  are  bases  which  form  salts,  as  the  amines 
do,  by  direct  addition  of  acids;  and  the  hydrogen  of  the  amino- 
group  may  be  replaced  with  alkyl  groups  as  in  the  amines. 

Aminoethyl  alcohol,  whose  formula  is  used  above  as  an  illustra- 
tion, is  of  interest  as  the  compound  from  which  the  physiologically 
important  choline  (p.  134)  may  be  considered  a  derivative. 

Ammo-aldehydes,  the  simplest  of  which  is  aminoacetaldehyde, 
CH2NH2CHO,  and  amino-ketones,  have  been  made,  but  in  small 
number.  Muscarin,  a  very  poisonous  substance,  which  is  found 
in  toad-stools  and  certain  other  plants,  is  apparently  a  quaternary 
base  related  to  aminoacetaldehyde,  and  having  the  formula, 

/N(CH3)3OH 
CH<  ,  H20 

XCHO 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  252 

Amino-acids 

Acids  in  which  the  amino  group  has  replaced  hydrogen  in  the 
alkyl  radical  of  the  acid  are  of  great  physiological  importance, 
since  many  of  them  are  natural  decomposition  products  of  the  pro- 
teins (cf.  p.  405).  They  may  be  considered  as  amines  in  which 
alkyl  hydrogen  has  been  replaced  by  the  carboxyl  group,  and,  in 
fact,  they  show  amine  as  well  as  acid  characteristics:  but  on  the 
whole  it  is  simpler  to  view  them  as  substituted  acids. 

Formation.  —  They  may  be  made:  i.  By  the  action  of  ammonia 
on  the  monohalogen  acid.  Thus  chloracetic  acid  yields  NH2  .  CH2  .- 
CO.OH,  NH(CH2.CO.OH)2,  and  N(CH2.CO.OH)3.  The  reac- 
tions are  like  those  for  forming  amines  from  the  alkyl  halides,  and, 
as  in  that  case,  the  immediate  products  are  substituted  ammo- 
nium salts  from  which  the  amino-acids  are  set  free  by  the  action 
of  alkalies. 

If  amines  (substituted  ammonias)  are  used  instead  of  ammonia, 
the  products  are  correspondingly  substituted  amino-acids, 
thus: 

CH3NH2  +  CH2C1.CO.OH  =  (CH3.NH)CH2CO.OH 

Methyl  ammo-acetic  acid 

2.  a-  Amino-acids  are  also  produced  from  aldehydes  or  ketones  by 
forming  first  the  hydrocyanic  acid  addition  product  of  these 
compounds  (p.  78),  replacing  the  hydroxyl  group  with  the  amino 
group  by  ammonia,  and  finally  converting  the  cyanogen  group 
into  the  carboxyl  group  by  hydrolysis: 


CH3      HCN  CH3  NHs    CHs  2HaO 

I         -  >  I    /OH  -  >  |    /NH2  --  >  | 
CHO          CH<  CH<  (HC1)CH(NH2) 

XCN  XCN  | 

CO.OH 

Acetaldehyde  Lactonitrile  o-Amino-  ot-Amino- 

propionitrile  propionic  acid 

(alanine) 


253  SOME   HALOGEN  AND  AMINO   DERIVATIVES 

The  amino-acids  may  be  obtained  in  a  pure  state  by  means  of 
their  copper  salts.  These  are  made  by  boiling  the  solutions  of  the 
acids  with  copper  carbonate,  and  crystallize  from  the  hot  solu- 
tions. The  copper  is  replaced  by  hydrogen  by  treatment  with 
hydrogen  sulphide. 

Properties.  —  The  amino-acids  are  crystalline  substances,  most 
of  which  are  readily  soluble  in  water,  but  insoluble  or  sparingly 
soluble  in  alcohol  or  ether.  Some  of  them  have  a  sweet  taste. 

While,  as  we  have  seen,  the  presence  of  the  strongly  negative 
halogens  greatly  increases  the  acid  character  of  acids,  the  decidedly 
positive  amino  group  opposes  the  acidity,  so  that  the  amino-acids 
are  neutral  compounds,  forming  salts  both  with  bases  and  with 
acids.  With  oxides  or  hydroxides  of  the  heavy  metals  they  give 
salts  in  which  the  hydrogen  of  carboxyl  is  replaced  by  the  metal; 
but  no  crystallizable  salts  with  sodium,  potassium,  or  barium  are 
formed.  With  acids  the  salts  are  like  those  of  the  amines  —  sub- 
stituted ammonium  salts.  It  also  appears  probable  from  some 
of  their  behavior  that  the  amino-acids  may  form  cyclic  salts  by 
reaction  between  the  carboxyl  and  amino  groups: 


/NH2  / 

CH3.CH<       =  CH3.CH<      O 
XCO.OH         ^CQ/ 

Reactions.  —  The  amino-acids  give  most  of  the  reactions  of  the 
amines.  Thus  with  nitrous  acid  the  amino-group  is  replaced  by 
hydroxyl  as  in  the  case  of  primary  amines  (p.  131),  and  alkyl  and 
acyl  chlorides  replace  the  hydrogen  of  the  amino-group  with  their 
radicals.  Esters  of  the  amino-acids  are  made  by  the  ordinary 
method  of  leading  hydrogen  chloride  into  a  mixture  of  the  acid 
and  alcohol.  The  hydrochloride  of  the  amino-ester  which  is  thus 
produced  gives  the  ester  by  treatment  with  a  solution  of  potas- 
sium hydroxide  at  a  low  temperature  and  immediately  extracting 
the  ester  with  ether.  In  other  reactions  the  relative  positions  of 
the  amino  and  carboxyl  groups  influence  the  result,  as  in  the  cases 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  254 

of  the  hydroxyl  and  halogen-substituted  acids.  The  a-compounds 
readily  give  anhydride  compounds  by  the  loss  of  water  from  two 
molecules: 


CH2NH2.CO.OH  ,NH  -  CO 


-  2H2O  =        ; 
CH2NH2.CO.OH  XCO  -  NET 

The  /3-acids  easily  lose  ammonia  with  the  formation  of  unsat- 
urated  acids: 

CH2NH2.CH2.CO.OH  =  CH2:CH.CO.OH  +  NH3 

/3-Amino-propionic  acid  Acrylic  acid 

The  7-amino-acids,  like  the  7-amino-hydroxy  acids  give  inner 
anhydrides  called  lactams,  on  account  of  their  similarity  to  the 
lactones  (p.  172). 

CH2NH2.CH2.CH2.CO.OH  =  CH2NH.CH2.CH2CO  +  H2O 

-y-Amino-butyric  acid  j  _  [ 

Lactam 

Among  the  amino-acids  and  their  derivatives  the  following  may 
be  given  as  examples. 

Aminoacetic  acid,  CH2NH2  .  CO  .OH,  which  is  also  called  glycine 
and  glycocoll,  may  be  made  from  monochloracetic  acid  and  ammo- 
nia. It  is  obtained  from  glue  and  other  proteins  by  boiling  with  di- 
lute sulphuric  acid,  and  from  hippuric  acid  (p.  359)  by  hydrolysis. 
From  its  aqueous  solution  crystals  are  obtained,  which  melt  with 
decomposition  at  232°.  Glycine  has  a  sweet  taste,  which  together 
with  its  production  from  glue,  was  the  occasion  for  the  name  gly- 
cocol  (y\vKvs  and  KoXXa).  Like  many  amino-acids  it  forms 
a  blue  copper  salt  when  its  solution  is  boiled  with  copper  carbon- 
ate. This  salt  is  very  sparingly  soluble  in  water,  and  crystallizes 
with  one  molecule  of  water. 

Sarcosine  is  methylaminoacetic  acid,  CH2NH(CH3).CO.OH, 
which  was  first  obtained  from  creatine 


/NH2 
HN—  C< 

XN(CH3).CH2.CO.OH 


t 

255  SOME   HALOGEN  AND  AMINO  DERIVATIVES 

a  subtance  contained  in  meat  extract,  and  related  to  guanidine  (p. 
233).  It  can  also  be  obtained  from  caffeine,  and  can  be  synthe- 
sized from  methylamine  and  monochlor-acetic  acid.  Betame,  which 
is  found  in  the  molasses  of  beet  sugar,  is  a  derivative  of  trimethyl 
glycine,  being  an  inner  ammonium  salt,  N(CH3)3.CH2.CO.O 

j [ 

Betame  is  the  source  of  the  "trimethyl  amine"  obtained  by 
the  destructive  distillation  of  vinasse  (cf.  p.  213). 

Alanine,  CH3.CHNH2.CO.OH,  or  a-amino-propionic  acid; 
leucine,  CH(CH3)2.CH2.CHNH2.CO.OH,  or  a-amino-isobutyl- 
acetic  add',  ly sine,  CH2NH2.(CH2)3.CHNH2.CO.OH,  a,ediamino 
caproic  acid,  are  illustrations  of  amino-acids  obtained  by  the 
hydrolysis  of  proteins. 

Asparagine,  which  is  found  in  asparagus  and  often  is  present  in 
sprouting  seeds  and  in  many  plants,  is  at  once  an  amino-  and  an 
amido-compound,  being  amino-succinic  acid  amide. 

CH2.CO.OH 

HNH2.CO.NH2 

That  this  is  the  structure  of  asparagine  is  shown  by  the  fact  that 
on  hydrolysis  it  gives  aspartic  acid, 

CH2.CO.OH 

,    CH.NH2.CO.OH 

whose  structure  is  proved  by  its  conversion  into  malic  acid,  (p.  185), 
CH2.CO.OH 

CHOH.CO.OH 

by  nitrous  acid. 

Like  many  amino-acids  and  their  derivatives,  these  compounds 
all  contain  an  asymmetric  carbon  atom  and  are  optically  active. 


INTRODUCTION  TO   ORGANIC   CHEMISTRY  256 

Asparagine  from  most  natural  sources  is  levo-rotatory;  but  from 
one  source  (the  sprouts  of  vetches)  two  sets  of  asparagine  crys- 
tals are  obtained  whose  solutions  have  opposite  rotatory  power. 
No  crystalline  racemic  form  has  been  obtained.  It  is  note- 
worthy that  the  dextro-asparagine  has  a  sweet  taste,  while 
that  of  the  levo-compound  is  disagreeaable  and  cooling. 


CHAPTER  XIX 
CYCLO-PARAFFINS 

In  several  instances  in  inorganic  chemistry  and  also  among  the 
organic  substances  already  studied,  the  student  has  met  with 
formulas  in  which  the  atoms  are  united  in  closed  rings,  such  as, 


O  Nv  CH2v  CH2.C(X 

'X,       ||  >0,       |     >>,       |  >0 

— O        N/  CH/  CH2.C(X 


/\ 

O  -  O 

Ozone  Nitrous  Ethylene  Succinic 

oxide  oxide  anhydride 


CH2.CO 

2\  /  \ 

>NH  ,  (X(  >0 


CH,CH 

Succinic  Glycollide 

imide 

But  no  compounds  have  thus  far  been  discussed  whose  formulas 
contain  a  ring  of  carbon  atoms  alone.  Such  compounds,  however, 
are  known,  and  among  them  are  a  very  large  number  of  the  most 
important  substances  of  organic  chemistry  —  those  which  form  the 
subject  of  the  second  part  of  this  book  under  the  title  of  the 
Aromatic  Compounds. 

Compounds  which  have  the  closed-ring  structure  are  called 
cyclic  compounds  —  isocyclic  when  the  ring  is  composed  of  atoms  of 
one  element  alone  as  in  ozone,  and  heterocyclic  if  the  elements  are 
different  as  in  the  other  illustrations  given  above. 

Certain  carbocyclic  (isocyclic)  compounds  which  are  inter- 
mediate in  their  deportment  between  the  open-chain  aliphatic 
compounds  and  those  of  the  aromatic  group  will  be  briefly  con- 
sidered here.  These  carbocyclic  hydrocarbons  are  composed  of 
methylene  radicals,  CH2,  and  are  known  as  the  cycloparaffins. 
Their  names,  formulas,  and  boiling  points  are  given  in  the 
following  table,  which  also  includes  for  comparison  the  boiling 
points  of  the  paraffins  and  defines  having  the  same  number  of 

257 


INTRODUCTION   TO   ORGANIC   CHEMISTRY 


258 


carbon  atoms.  It  will  be  noticed  that  in  every  case  the  boiling 
point  of  the  cyclic  compound  (polymethylene)  is  the  highest  of 
the  three. 


Trimethylene  or 
cyclopropane 

|     2\CH2 
CH/ 

Tetramethylene, 
cyclobutane 

CH2.CH2 

1        1 
CH2.CH2 

Pentamethylene, 
cyclopentane 

CH2.  CH2x 

1         >ci 

CH2.CH/ 

Hexamethylene, 

CH2.CH2.CH2 

Poly- 
methylene 


-35 


cyclohexane 

Heptamethylene, 
cycloheptane 


CH2.CH2.CH2 
CH2.CH2.CH2v 

I 
CH2.CH2.CH/ 

CH2.CH2.CH2.CH2 


CH2 


49 


81 


117 


Olefine     Paraffin 


-  48°       -  45C 


-    5 


40 


69 


95 


98 


Nonomethylene, 
cyclononane 


>CH2 


146 


171 


126 


150 


Octomethylene, 

cyclooctane  |  | 

CH2.CH2.CH2.CH2 

CH2.CH2.CH2.CH2V 

1  /( 

CH2.CH2.CH2.CH/ 

The  cycloparaffins  are  isomeric  with  the  unsaturated  hydro- 
carbons of  the  ethylene  series  (olefines),  but  differ  from  them  in 
not  being  readily  oxidized  by  potassium  permanganate,  and  in 
forming  substitution  rather  than  addition  products,  so  that  their 
conduct  in  general  resembles  that  of  the  paraffins.  Unlike  both 
paraffins  and  defines,  the  series  of  polymethylenes  is  apparently 
limited  to  the  small  number  given  in  the  table,  and  there  are  theo- 
retical considerations  which  make  the  existence  of  larger  rings 
improbable.  Much  larger  heterocyclic  rings  are,  however,  known. 

The  argument  for  the  ring  formula  of  trimethylene  is  as  follows. 
It  is  formed  by  the  action  of  sodium  on  (i,3)-dibrompropane  (tri- 


259  CYCLO-PARAFFINS 

methylene  bromide)  whose  formula  is  known  to  be  that  used  in 
the  following  equation: 

CH2Br.CH2.CH2Br  +  2Na  =  CH2.CH2.CH2  +  2NaBr 

Trimethylene  bromide  Trimethylene 

Chlorine  forms  a  substitution  product,  C3H4C12.  Trimethylene 
is  more  stable  toward  bromine  than  is  its  isomer  propylene,  but 
in  sunlight  bromine  acts  additively,  forming,  however,  trimethyl- 
ene  bromide  again,  instead  of  propylene  bromide,  CH2Br .  CHBr .  - 
CH3,  which  would  be  the  product  of  bromine  on  propylene. 

Pentamethylene  can  be  made  by  the  following  steps  which  indi- 
cate its  structure: 

CH2.CH2.CO.(X  CH2.Ctf2\        HH  CHa.CH^ 

|  \Ca— »|  >CO— >|  >CH2 

CH2.CH2.CO.CK  CH2.CH/         HH  CH2.CH/ 

Calcium  Adipate  Ketopentamethylene         Pentamethylene 

Hexamethylene  will  be  discussed  later  under  the  aromatic 
compounds,  because  of  its  relationship  to  benzene.  Many  deriva- 
tives of  this  hydrocarbon  occur  in  nature,  particularly  in  the  ter- 
penes  and  in  camphor. 

Numerous  derivatives  of  the  cycloparaffins  have  been  prepared 
and  investigated,  most  of  them  being  made  much  more  readily 
than  the  hydrocarbons  themselves.  The  preparation  of  the  tetra-, 
octo-,  and  nonohydrocarbons  has  proved  especially  troublesome, 
and  it  is  only  quite  recently  that  they  have  been  obtained.  The 
penta-  and  hexamethylenes  are  the  most  stable  of  the  group,  and 
the  stability  decreases  from  this  maximum,  whether  the  number 
of  carbon  atoms  in  the  ring  is  increased  or  diminished. 

Stereochemistry  of  the  Cycloparaffins. — An  explanation  of  the 
different  degrees  of  stability  of  the  poly  methylene  compounds  and 
of  the  non-existence  of  rings  of  more  than  nine  carbon  atoms  is 
offeredin  the  "strain  theory  "of  A.  v.Baeyer  (1885).  This  theory 
is  in  brief  as  follows:  In  the  tetrahedral  structure  of  which  the 
carbon  atom  is  the  center,  the  valencies  or  affinities  of  that  atom 
are  supposed  to  be  directed  to  the  solid  angles  of  the  figure,  along 
the  axes  of  the  tetrahedron.  When  several  carbon  atoms  are 


INTRODUCTION  TO   ORGANIC   CHEMISTRY 


260 


united  in  chains  or  in  rings,  the  condition  for  the  greatest  stability 
is  when  the  valencies  connecting  each  pair  of  neighboring  carbon 
atoms  are  in  a  straight  line.  If  this  condition  is  unfulfilled  and  the 
directions  of  the  valencies  make  an  angle  with  each  other,  the  con- 
figuration becomes  less  stable  as  this  angle  (of  180°)  becomes  less, 
because  of  the  "strain"  which  results  from  the  deflection  that  the 
valencies  suffer  in  coming  together. 

In  open-chain  compounds — the  paraffins — the  linkages  occur 
without  deflection  of  the  valencies  from  their  normal  directions, 
but  the  result  is  that  in  these  compounds  the  carbon  atoms  do  not 
lie  in  a  straight  line  (as  represented  in  the  usual  formulas),  but  in 
a  regular  zigzag  whose  equal  angles  are  those  which  the  edges  of  a 
regular  tetrahedron  subtend  at  its  center,  or  109°  28'.  Thus  the 
formula  for  normal  pentane  would  be 

HI  K  H 


FIG.  i. — Normal  pentane. 


FIG.  2. — Baeyer's  strain  theory. 


2  6 1  C  YCLO-P  ARAFFINS 

Figure  2  gives  the  normal  directions  of  valencies  in  ring  for- 
mations of  from  three  to  five  atoms  of  carbon. 

Supposing  that  in  trimethylene  the  centers  of  the  three  carbon 
atoms  lie  in  the  angles  of  an  equilateral  triangle,  the  directions 
of  the  linking  valencies  from  each  carbon  atom  must  be  at  an 
angle  of  60°  with  each  other.  Since  the  normal  directions  of  the 
valencies  would  make  an  angle  of  109°  28',  this  configuration 
requires  that  each  valence  shall  be  "strained"  24°  44'  from  its 
normal  direction  since  109°  28'—  60°  =  49°28'  =  2  X  24°  44'.  In 
the  tetramethylene  ring  with  the  four  carbon  atoms  at  the  angles 
of  a  square,  the  deviation  of  each  of  the  valencies  is  9°  44'  (109° 
28'  —  90°  =  19°  28'  =  2  X  9°  44') .  In  pentamethylene  the  angle 
of  strain  would  be  o°  44';  in  hexamethylene,  —5°  i6';and  becomes 
larger  in  the  higher  cycloparaffins.  Thus  the  greater  stability  of 
the  five-  and  six-carbon  atom  rings  is  "explained." 

This  theory  also  accounts  for  the  non-existence  of  anhydrides  of 
oxalic  and  malonic  acids,  and  the  ready  formation  of  succinic  and 
glutaric  anhydrides  with  chains  of  four  and  five  atoms  of  carbon 
linked  into  rings  by  an  atom  of  oxygen.  In  accord  with  the  the- 
ory, too,  is  the  fact  that  no  anhydrides  of  adipic  acid,  (CH2)4- 
(CO.OH)2,  or  of  higher  dicarboxylic  acids  exist.  The  readiness 
with  which  7-  and  5-lactones  and  lactams  are  produced  is  also  in 
agreement  with  the  theory. 


PART  II 

AROMATIC  COMPOUNDS  AND 
RELATED  SUBSTANCES 


CHAPTER  XX 

AROMATIC  HYDROCARBONS 
Benzene  and  Its  Homologues 

The  substances  that  belong  to  the  so-called  aromatic  group 
comprise  the  majority  of  those  known  to  organic  chemistry.  The 
name  of  the  group  was  first  applied  to  certain  natural  vegetable 
substances  which  possess  an  agreeable,  aromatic  odor,  such  as 
the  oil  of  bitter  almond  and  of  wintergreen.  It  has  persisted 
like  many  of  the  older  names,  being  the  common  designation  of  a 
large  group  of  compounds  which,  though  often  without  the  charac- 
teristic aromatic  odor,  are  chemically  related  to  those  first  classed 
under  this  name.  Certain  well-marked  peculiarities  in  chemical 
deportment,  in  which  the  aromatic  compounds  differ  from  those  of 
the  aliphatic  group,  justify  a  separate  classification  and  treatment. 
Every  aromatic  compound  contains  at  least  six  carbon  atoms; 
and  one  of  the  most  significant  of  the  peculiarities  of  these 
compounds  is  that,  when  one  of  them  has  more  than  six  carbon 
atoms,  it  can  be  broken  down  into  one  which  contains  six,  and 
at  this  point  farther  decomposition  is  resisted. 

Benzene,  CeHe,  is  the  simplest  of  the  hydrocarbons  of  this 
group  and  may  be  regarded  as  the  parent  substance  from  which 
all  the  others  are  derived.  It  was  discovered  in  1825  by  Faraday 
in  the  liquid  found  in  compressed  oil  gas,  and  found  by  A.  W. 
Hofmann  twenty  years  later  in  the  mixture  of  light  oils  distilled 
from  coal  tar,  and  is  obtained  from  this  latter  source. 


266  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

Coal  tar  is  formed  in  the  destructive  distillation  of  bituminous 
coals  in  the  coal  gas  and  coke  industries,  which  is  carried  out  at 
temperatures  from  Q8o0-iioo°.  It  is  a  black,  viscous  oil,  owing 
its  color  chiefly  to  the  presence  of  finely  divided  carbon.  When 
distilled,  less  than  half  of  it  is  volatilized,  leaving  a  residue  of 
pitch  which  is  used  as  a  black  varnish  for  metals  and,  mixed  with 
asphalt,  for  making  pavements.  The  distillate  is  collected  in 
separate  fractions,  the  temperature  being  carried  up  to  about 
300°.  The  substances  obtained  in  this  way  are  of  three  classes: 
indifferent  hydrocarbons  not  affected  by  dilute  acids  or  alkalies, 
acid  compounds  which  dissolve  in  alkalies,  and  bases  which  dis- 
solve in  acids.  By  successive  treatment  with  alkalies  and  acids 
a  separation  of  these  classes  is  effected,  and  by  further  operations, 
more  limited  groups  of  substances,  or  individual  compounds  are 
obtained.  Of  the  many  compounds  contained  in  the  coal  tar 
distillates,  only  a  few — benzene,  toluene,  naphthalene,  anthracene, 
and  phenol — are  produced  commercially  in  a  pure,  ore  vqn  approxi- 
mately pure,  condition.  Mixtures  of  isomeric  compounds  are 
also  obtained,  known  as  xylols  and  cresols;  and  mixtures  of  homo- 
logues — the  pyridine  and  other  bases.  Small  amounts  of  other 
compounds  containing  oxygen,  sulphur,  and  nitrogen,  are  also 
obtained.  The  amount  of  benzene  and  toluene  is  usually  about 
1-1.5  Per  cent,  of  the  tar,  of  anthracene  0.25-0.45  per  cent.,  of 
phenol  0.4-0.5  per  cent.,  of  cresols  2-3  per  cent.,  and  of  naphtha- 
lene o-io  per  cent. 

Benzene  obtained  from  this  source  contains  very  small  amounts 
of  thiophene  (p.  394),  which  cannot  be  removed  by  distillation, 
but  is  extracted  by  shaking  the  benzene  with  concentrated  sul- 
phuric acid.  -  The  final  purification  of  the  benzene  is  effected  by 
crystallizing  it  in  a  freezing  mixture. 

Benzene  is  a  thin  oil,  lighter  than  water,  which  has  a  slight, 
not  unpleasant  odor,  melts,  when  frozen,  at  5. 4°,  and  boils  at  80.4°. 
It  is  insoluble  in  water. 

Formation. — Benzene  is  formed,  together  with  some  related 


AROMATIC  HYDROCARBONS  267 

hydrocarbons,  when  acetylene  is  led  through  tubes  heated  to  a 
dull  red.  Benzene  can  in  this  way  be  synthesized  from  the  ele- 
ments, and  another  synthesis  of  this  sort  can  be  made  through 
mellitic  acid  (p.  370).  In  these  ways  and  others,  it  is  possible  to 
convert  simple  aliphatic  compounds  into  substances  of  the  aro- 
matic group.  Benzene  can  also  be  made:  i.  From  benzoic  acid, 
CeH5.CO.OH,  by  heating  sodium  benzoate  with  sodium  hydrox-j 
ide  or  soda-lime,  a  reaction  similar  to  that  by  which  aliphatic 
hydrocarbons  are  formed  from  acids: 

C6H5.CO.ONa  +  NaOH  =  C6H6  +  Na2CO3 
2.  From  phenol,  CeHs.OH,  by  distillation  with  zinc  dust.  3. 
From  benzene  sulphonic  acid,  C6H6.SO3H,  by  superheated  steam, 
or  boiling  with  hydrochloric  acid.  4.  From  amidobenzene  (ani- 
line), C6H5NH2,  by  conversion  into  the  corresponding  diazo 
compound  (p.  315)  and  boiling  with  alcohol.  5.  From  halogen 
derivatives  by  the  Grignard  reaction  (cf.  p.  274). 

These  four  methods  are  general  ones  for  the  exchange  of  these 
different  groups  for  hydrogen  in  the  aromatic  compounds. 

Formula  of  Benzene. — The  molecular  formula  for  benzene, 
established  by  analysis  and  the  determination  of  its  vapor  density, 
is  CeHe.  This  means  that  of  the  twenty-four  valencies  of  the  six 
carbon  atoms  only  sixteen  are  necessary  for  the  single  linkage 
of  these  atoms  if  the  atoms  form  an  open  chain,  or  eighteen  if  the 
compound  is  cyclic,  and  suggests  a  high  degree  of  unsaturation. 
The  same  thing  is  true  of  dipropargyl  which  is  also  C6He.  But 
while  dipropargyl  shows  itself  to  be  a  highly  unsaturated  com- 
pound (p.  50)  benzene  differs  markedly  in  its  chemical  conduct 
from  this  substance  and  the  other  unsaturated  compounds  we  have 
studied.  It  is  exceedingly  indifferent  toward  oxidizing  agents, 
not  decolorizing  permanganate,  and  resisting  attacks  which  would 
break  down  ordinary  unsaturated  hydrocarbons  into  compounds 
of  a  less  number  of  carbon  atoms.  Further,  it  does  not  unite 
additively  with  certain  reagents  as  the  unsaturated  compounds 


268  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

do  so  readily;  for  instance,  with  hydrogen  bromide,  or  hypochlor- 
ous  or  sulphuric  acid.  With  the  free  halogens,  however,  it  does 
form  addition  products  in  sunlight,  but  much  less  readily  than  the 
hydrocarbons  of  unsaturated  groups;  and  hydrogen  can  also 
be  added  to  it  under  certain  conditions.  But  the  maximum  num- 
ber of  added  atoms  in  either  case  is  six,  giving  CeHeBre  and  CcHi2, 
while  the  corresponding  aliphatic  compounds  from  unsaturated 
hydrocarbons  are  CeHeBrg,  and  CeHu.  In  this  last  respect,  there- 
fore, benzene  differs  both  from  the  unsaturated  hydrocarbons, 
and  from  the  paraffins  which  form  no  addition  products.  It 
differs  from  the  paraffins  also  by  the  readiness  with  which  nitro- 
substitution  products  are  made  by  the  action  of  concentrated 
nitric  acid: 


HONO2  =  C,H.^O2  +  H2O 

Nitrobenzene 


and  sulphonic  acids  by  concentrated  sulphuric  acid: 


CeHe+HO.SCVOH  =  CeH^SCVOH  +  H2O 

Benzene  sulphonic  acid 

And,  further,  the  behavior  of  the  various  derivatives  of  benzene  is 
quite  unlike  that  of  corresponding  substitution  products  of  the 
open-chain  hydrocarbons  we  have  studied.  The  stability  and  per- 
sistence of  the  benzene  nucleus  of  six  carbon  atoms  in  aromatic 
compounds  led  Kekule  in  1865  to  propose  a  closed-ring  forma- 
tion in  explanation  of  its  peculiarities  and  its  differences  from 
the  open-chain  aliphatic  compounds. 

Facts  helpful  in  suggesting  the  structure  of  the  benzene  mole- 
cule are  found  in  the  number  of  substitution  products  it  forms  with 
a  given  element  or  group,  i.  It  has  proved  impossible  to  obtain 
more  than  one  monosubstitution  product,  and  the  results  of 
elaborate  experiments  have  shown  that  each  of  the  six  hydro- 
gen atoms  bear  the  same  relation  to  the  rest  of  the  molecule.  A 


AROMATIC  HYDROCARBONS  269 

formula  in  which  the  six  carbon  atoms  are  linked  in  a  closed  ring 
is  the  only  one  by  which  this  symmetry  can  be  expressed. 

H 

C 

/\ 

HC      CH 

I        I 
HC      CH 


Y 


H 

2.  If  more  than  one  hydrogen  atom  in  benzene  is  replaced  by 
the  same  element  or  group,  it  is  found  that  three  a^id  only  three 
isomeric  substitution  products  can  be  obtained  when  two,  three, 
or  four  atoms  of  hydrogen  are  replaced;  and  only  one  product 
when  five  or  six  are  replaced.  These  facts  are  accounted  for  by 
the  symmetrical  ring  formula.  In  the  following  formulas  which 
show  this,  we  adopt  the  conventional  expression  for  the  benzene 
molecule  as  an  unlettered  hexagon.  At  each  angle  the  group  CH 
is  assumed  unless  some  symbol  appears,-  and  in  this  case  it  indi- 
cates the  replacement  of  the  hydrogen  alone  by  some  atom  or 
group.  The  angles  (carbon  atoms)  are  numbered  for  readier  ref- 
erence in  the  discussion. 

The  five  possible  arrangements  with  two  substitutes  are: 

X  X  X  X  X 


It  is  evident  that  the  positions  i,  2  and  i,  6  are  identical  so  far 
as  relations  of  the  substituents  to  each  other  and  the  rest  of  the 


270  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

molecule  are  concerned.  The  same  is  true  of  the  positions  i,  3 
and  i,  5.  Formulas  i  and  5  are  therefore  the  same,  and  formulas 
2  and  4  also  represent  the  same  compound,  leaving  three  different 
disubstitution  products  shown  by  formulas  i  or  5,  2  or  4,  and  3. 

The  three  types  of  disubstitution  products  are  designated  as 
ortho,  when  the  substituents  are  on  adjacent  carbon  atoms,  i,  2  or 
1,6;  meta,  when  in  the  positions  i,  3  and  i,  5,  and  para  when  on 
opposite  carbon  atoms,  i,  4. 

With  three  like  substituents  the  student  will  readily  see  that, 
again,  only  three  distinct  structures  can  be  formulated.  These 
are  shown  in  the  following  formulas  with  the  names  which  are 
given  them: 


X 


Adjacent  i,  2,  3  Unsymmetrical  i,  2,  4  Symmetrical  i,  3,  5 

When  there  are  four  like  substituents,  there  are  also  three  and 
only  three  isomers  possible.  If  in  this  case  we  may  regard 
the  two  remaining  hydrogen  atoms  as  the  substituents  in  a 
molecule  of  CeXe,  the  demonstration  becomes  identical  with  that 
for  the  disubstitution  products. 

With  five  like  substituents,  it  is  evident  that  there  can  be  but 
one  arrangement,  and  the  same  is,  of  course,  true  when  all  the 
hydrogen  is  replaced  by  like  atoms  or  groups. 

If,  however,  the  substituting  atoms  or  groups  are  different,  it  is 
obvious  that  the  numbers  of  isomers  may  be  much  larger  when 
three  or  more  hydrogen  atoms  are  replaced. 

A  symmetrical  ring  formula  is  thus  seen  to  allow  the  successful 
representation  of  the  possibilities  and  limitations  of  the  isomerism 
which  is  established  by  experiment.  The  student  has  probably 
noticed  that  the  formulas  which  have  been  given  have  represented 


AROMATIC  HYDROCARBONS 


271 


carbon  as  a  triad,  or  at  least  have  not  indicated  the  disposal  of  its 
fourth  valency.  In  fact,  this  is  still  an  open  question,  but  in  the 
great  majority  of  aromatic  compounds  it  is  a  matter  of  compara- 
tively little  importance,  since  in  most  of  the  reactions,  the  fourth 
bond,  whatever  its  nature,  remains  undisturbed.  It  is  only  in 
the  halogen  and  hydrogen  addition  products  that  it  must  be 
reckoned  with,  and  here  it  is  only  necessary  to  assume  that  each 
carbon  atom  has  one  additional  valence  which  is  disposable  under 
certain  conditions.  From  a  theoretical  point  of  view,  however, 
the  question  is  of  great  interest,  and  many  suggestions  have  been 
made,  none  of  which  are  free  from  objections.  The  first  struc- 
tural formula  for  benzene  was  proposed  by  Kekule  in  1865  in  the 
form  shown  in  i,  with  alternate  double  and  single  bonds, 

H 
C 


HC      CH 

I         II 
HC       CH 

V 

c 

H 

i 

Kekute 


The  chief  objection  to  this  is  that  the  positions  i,  2  and  i,  6  are 
not  identical  and  that  there  should  therefore  be  two  ortho  com- 
pounds. To  meet  this  criticism  Kekule  assumed  that  the  linkages 
between  the  carbon  atoms  were  dynamic  instead  of  static,  and 
that  the  double  and  single  unions  are  continually  shifting  their 
places.  In  the  Claus  formula  the  fourth  valencies  are  utilized 
in  binding  opposite  atoms,  while  in  the  "centric"  formula  of 
Baeyer,  they  "neutralize"  each  other  without  actually  uniting, 
and  thus  render  no  service  in  holding  the  ring  together,  but 
may  be  utilized  in  the  case  of  addition  products.  The  objec- 


272  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

tions  to  these,  and  to  other  formulas  which  have  been  proposed, 
gain  in  force  when  the  spatial  arrangement  of  the  atoms  is 
considered. 

The  solution  of  the  problem  of  the  structure  of  the  benzene 
molecule,  which  Kekule  gave  in  1865,  in  his  hexagonal  formula, 
has  had  the  most  profound  influence  on  the  development  of 
organic  chemistry.  It  led  at 'once  to  an  understanding  of  the 
relations  of  the  aromatic  compounds  to  benzene  and  to  each  other, 
and  has  guided  the  wonderful  synthetic  achievements  in  this 
group  of  substances.  It  is  probably  the  most  fruitful  single  idea 
in  the  history  of  chemistry  since  Dal  ton's  atomic  theory. 

It  has  been  stated  that  benzene  reacts  directly  with  nitric  acid, 
sulphuric  acid,  chlorine,  and  bromine,  with  the  formation  of 
compounds  in  which  one  or  more  hydrogen  atoms  of  the  benzene 
molecule  are  replaced  by  the  nitro  group,  NC>2,  the  sulphonic  acid 
group,  SO3H,  or  by  the  halogens.  If  we  add  to  this  that  halogen 
derivatives  of  the  aliphatic  hydrocarbons  react  with  benzene  in 
the  presence  of  aluminium  chloride  with  the  substitution  of  the 
aliphatic  radical  for  hydrogen,  the  list  of  direct  substitutions  is 
practically  exhausted.  Other  products  in  which  amido,  hydroxyl, 
carboxyl,  and  other  groups  are  present,  may  be  made  from  these 
directly  substituted  compounds. 

The  monad  group,  CeH5,  which  appears  in  all  monosubstituted 
benzenes,  is  called  phenyl  (from  phenol,  CeHe.OH,  in  which  it  is 
united  to  hydroxyl),  and  this  term  is  commonly  employed  in  the 
naming  of  compounds;  thus,  CeH^Cl  is  phenyl  chloride,  C^R^C^H.^ 
is  diphenyl,  etc.  The  general  name  aryl  is  used  for  phenyl  and  the 
other  homologous  monad  radicals  of  the  aromatic  group.  For 
the  sake  of  convenience  in  .our  discussions  we  will  further  desig- 
nate the  divalent,  trivalent,  etc.,  groups,  CeH4,  CeHs,  etc.,  and 
those  in  which  partial  substitution  has  occurred,  such  as  Br.C<jH4, 
etc.,  which  appear  in  benzene  derivatives,  as  cyclic  radicals  in 
distinction  to  the  "side-chain"  or  aliphatic  radicals  which  are 
present  in  many  of  the  hydrocarbons  of  the  aromatic  group. 


AROMATIC  HYDROCARBONS  273 

Homologues  of  Benzene 

A  considerable  number  of  hydrocarbons  is  known  which  are 
related  to  benzene  and  to  each  other  in  such  a  way  that,  like  the 
paraffins,  they  form  an  homologous  series,  with  the  general  for- 
mula, CnH2n_6.  The  empirical  formulas  of  these  hydrocarbons 
are,  therefore,  CyHs,  CsHio,  CgHi2,  etc.,  showing  an  increment 
from  member  to  member  of  CH2,  and  an  increase  of  fourteen  in 
molecular  weight,  as  in  the  homologous  series  of  the  aliphatic 
group. 

These  hydrocarbons  all  contain  the  benzene  ring  with  one  or 
more  atoms  of  hydrogen  replaced  by  alkyl  groups,  so  that  their 
structure  is  given  by  such  formulas  as,  CeHs.CHs,  CeH^CHaJs, 
CeH5.C2H5,  etc.  That  these  formulas  represent  their  constitu- 
tion becomes  evident  from  the  methods  by  which  they  may  be 
formed,  and  by  their  reactions. 

Formation  of  the  Homologues  of  Benzene. — The  most  impor- 
tant methods  for  the  replacement  of  hydrogen  in  benzene  be 
alkyl  groups  are  the  following: 

i.  The  Fittig  synthesis,  which  is  an  application  of  the  Wurtz 

method  for  the  synthesis  of  paraffins  (p.  28).     It  consists,  like 

the  latter,  in  treating  a  solution  of  the  halides  (here  a  mixture  of 

the  halogen  substituted  benzene  and  the  alkyl  halide)  with  sodium: 

CeH^Br  +  CH3I  +  2Na  =  CeHs.CH,  +  NaBr  +  Nal 

Brombenzene  Toluene 

C6H4Br2  +  2CH3I  +  4Na  =  C6H4(CH3)2  +  2NaBr  +  2NaI 

Dibrombenzene  Xylol 

In  a  similar  way  additions  may  be  made  to  the  side  chain  already 
present  by  using  halogen  derivatives  of  benzene  homologues: 
C6H6.CH2Br  +  CH2Br.CH2.CH2.CH3  +  2Na  = 

Benzyl  bromide  Butylbromid 

C6H5.CH2.CH2.CH2.CH2.CH3.  +  2NaBr 

Amylbenzene 

In  certain  instances  zinc  or  silver  may  be  used  in  place  of  sodium. 
These  reactions  give  the  clearest  evidence  of  the  constitution  of 
these  compounds. 


274  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

2.  Friedel,  and  Crafts  Synthesis. — In  the  presence  of  anhydrous 
aluminium  chloride,  halogen  derivatives  of  the  aliphatic  hydro- 
carbons react  with  benzene: 

AlCli 

C6H6  +  CH3C1  =  C6H5CH3  +  HC1 

Toluene 

The  action  is,  however,  not  limited  to  the  formation  of  a  single 
alkyl  benzene,  for  some  of  that  first  formed  reacts  with  the  alkyl 
chloride  to  form  the  dialkyl  benzene,  and  this  in  turn  is  partly 
converted  into  the  trialkyl  compound.  Consequently  a  single  alkyl 
benzene,  as  indicated  in  the  above  equation,  is  not  obtained  by  this 
reaction,  but  a  mixture  of  the  mono,  di,  tri,  etc.,  substituted  ben- 
zenes, which,  however,  can  usually  be  separated  by  fractional  dis- 
tillation. It  is  to  be  noted  that  this  reaction  does  not  occur  when 
the  halogen  atom  is  in  the  benzene  ring,  but  only  when  it  is  united 
to  an  alkyl  group.  Indeed,  it  appears  that  the  explanation  of  this 
reaction  is  to  be  found  in  the  formation  of  an  addition  compound 
of  benzene  with  the  aluminium  chloride,  as  an  intermediate  step. 
The  two  following  reactions  may  also  be  employed  for  making 
benzene  homologues. 

3.  Grignard's  Synthesis  (p.  36). — Magnesium  reacts  with  halo- 
gen substitution  compounds  of  benzene  as  it  does  with  the  corre- 
sponding paraffin  derivatives,  and  the  magnesium  compounds  are 
employed  for  a  variety  of  syntheses.     They  react  with  water  with 
the  production  of  the  corresponding  hydrocarbons: 

C6H5.MgBr  +  H2O  =  CeHe  +  MgOH.Br 
CeHg.CHa.MgBr  +  H2O  =  GeH^CHa  +  MgOH.Br 

4.  The  homologues  of  benzene  may  also  be  made  from  the 
corresponding  acids,  by  the  general  reaction  which  the  organic 
acids  undergo  when  heated   with    lime  or  sodium  hydroxide 
(p.  28): 

/CH3 
C6H4< 

XX). OH  +  CaO  =  C6H5.CH3  +  CaC03 


AROMATIC   HYDROCARBONS  275 

Reactions. — Since  the  homologues  of  benzene  are  compounds 
which  contain  hydrocarbon  groups  of  two  distinct  types — cyclic 
and  alkyl  radicals — they  give,  as  we  should  expect,  the  reactions  of 
both  types,  somewhat  modified  in  each  case  by  the  presence  of 
the  other  radical.  Such  persistence  of  type  characteristics  has 
become  familiar  from  our  study  of  the  aliphatic  group.  The 
hydrogen  of  the  alkyl  groups  is  replaced  by  chlorine  or  bromine  in 
sunlight  as  in  the  case  of  the  paraffins,  and  the  hydroxyl,  aldehyde, 
carboxyl,  amino,  and  other  groups  may  be  introduced  by  the  same 
reactions  employed  in  the  aliphatic  group.  The  resulting  com- 
pounds show  essentially  the  same  characteristics  and  behavior  as 
the  corresponding  derivatives  of  the  paraffins,  with  the  added 
possibilities  of  reactions  in  the  cyclic  group.  In  one  respect, 
however,  the  homologues  of  benzene  show  a  decided  difference 
from  the  paraffins:  while  the  paraffins  cannot  be  oxidized  readily, 
and  when  oxidized  do  not  yield  definite  fatty  acids,  the  alkyl 
groups  when  united  to  cyclic  radicals  are  easily  oxidized.  The 
oxidation  usually  results  in  the  conversion  of  the  side  chain, 
however  long,  into  a  single  carboxyl  group  which  remains  united 
to  the  cyclic  radical.  Thus  both  toluene,  CeHs-CHs,  and  propyl 
benzene,  CeHs.CgHT,  yield  benzoic  acid,  C6H5.CO.OH.  When 
the  hydrocarbon  has  two  or  more  side  chains,  a  corresponding 
number  of  carboxyl  groups  results  from  oxidation,  and  this  gives 
a  simple  method  for  determining  the  number  of  side  chains  which 
were  present.  When  dilute  nitric  acid  is  used  as  the  oxidizing 
agent,  if  two  or  more  side  chains  are  present,  one  or  more  may 
escape  oxidation.  Thus  ortho  and  para  xylenes,  CeH^CHs^, 
give  the  corresponding  toluic  acids,  C6H4(CH3)(CO.OH).  Chro- 
mic acid,  on  the  other  hand,  usually  effects  the  simultaneous 
oxidation  of  all  side  chains,  and  would  give  in  this  case  the  cor- 
responding dibasic  acids,  CeH4(CO.OH)2.  If  two  or  more  side 
chains  of  different  lengths  are  present,  the  longer  one  is  usually 
oxidized  first  by  nitric  acid.  Thus  by  the  oxidation  of  cymene 
(methylisopropyl  benzene,  CHs.CeH^.CaHT),  para  toluic  acid, 
CHs.CcHU-CO.OH,  is  formed,  as  the  first  product. 


276 


INTRODUCTION  TO   ORGANIC  CHEMISTRY 


The  hydrogen  of  the  cyclic  radical  can  be  directly  replaced  by 
the  same  elements  or  groups  as  the  hydrogen  of  unsubstituted 
benzene  and  in  the  same  way.  The  reactions,  however,  generally 
take  place  more  readily  with  the  homologues  of  benzene  than  with 
benzene  itself.  This  greater  reactivity  is  accounted  for  by  the 
fact  that  all  the  substituents  which  can  be  thus  directly  introduced 
are  negative  or  acidic  in  character,  while  the  alkyl  groups  are 
positive. 

BENZENE  AND  ITS  MOST  IMPORTANT  HOMOLOGUES 


Name                                                Formula                 ™%£* 

Boiling 
point 

Specific 
gravity 

C6H6,  Benzene.                               C6H6                     5  .  8° 

8o.2°0 

874(2o°/4°) 

CrHs,  Toluene.                                C6H6.CH3            —92.4 

III 

0.869(16°) 

o-Xylene 

/CH3  (i) 
U    4\CH,  (2)    ~ 

142 

0.893(9°) 

m-Xylene 

Dimethyl-               ^  ™ 
benzenes  CeH^p-.3  .  >     —53 

139 

0.881(0°) 

CsHi.0  ' 

v^ii3   \3/ 

p-Xylene 

/CH3(i) 
C6H<CH3(4)    +IS 

138 

0.880(0°) 

Ethylbenzene                      CcHs.CzHs         —92.8 

136 

0.883(0°) 

Hemelli- 

/CH3  (i) 

thene 

C6H/-CH3(2)    liquid 

175 

CH3  (3) 

Pseudo- 

Trimethyl               .CHj  (i) 

cumene 

benzenes   CeH3^CH3  (2)    liquid 

169.5 

0.895(0°) 

CH3  (4) 

C9Hu 

/CH3  (i) 

Mesitylene 

C6H/CH3(3)    liquid 

165 

0.865(14°) 

NCH3  (5) 

n-Propylbenzene                 C6H6.C3H7          liquid 

159 

0.867(14°) 

iso-Propylbenzeneor         CtH6.CH/CHs 
Cumene                                          \CH3 

153 

0.866(16°) 

'CH3  (i) 


Durene,  Tetramethyl- 
benzene 

Cymene,  Methyl-iso- 
propyl-benzene 


CH8  (5) 

/CH,  (i)  liquid     175 
C6±1\CH(CH3)2  (4) 


0.856(20°) 


AROMATIC   HYDROCARBONS  277 

All  these  hydrocarbons  (see  table),  with  the  exception  of  n- 
propyl-benzene  and  cymene,  are  found  in  the  distillates  from  coal 
tar.  With  the  exception  of  durene,  they  are  liquids  of  character- 
istic but  not  disagreeable  odors. 

Benzene  received  its  name  from  benzoic  acid  from  which  it  was 
obtained  in  1834  by  distillation  with  lime.  The  acid  in  turn  was 
named  from  gum  benzoin  from  which  it  was  obtained  as  a  subli- 
mate early  in  the  seventeenth  century.  Benzene  is  chiefly  used 
for  making  nitro-benzene  as  the  first  step  to  the  manufacture  of 
aniline  and  a  great  variety  of  technical  substances, 

Commercial  benzene  is  usually  a  mixture  of  benzene  and  toluene 
with  small  amounts  of  other  hydrocarbons;  and  the  benzene  prod- 
ucts which  are  obtained  as  fractional  distillates  from  coal  tar 
are  known  as  "90  per  cent."  and  "50  per  cent."  benzol.  These 
terms  mean  that  90  or  50  per  cent,  of  the  mixture  distils  below 
100°.  The  "90  per  cent,  benzol"  contains  about  70  per  cent, 
of  benzene  and  24  per  cent,  of  toluene,  and  the  "50  per  cent, 
benzol"  a  somewhat  less  amount  of  benzene  with  toluene  and 
xylenes. 

Toluene,  CyHs,  is  so  called  because  it  is  a  product  of  the 
dry  distillation  of  tolu  balsam.  Its  use  is  similar  to  that  of 
benzene. 

The  xylenes,  CsHio,  are  named  from  their  production  in 
the  destructive  distillation  of  wood  (£v\ov).  They  are 
now,  however,  obtained  entirely  from  coal  tar.  All  three 
isomers  occur  in  coal  tar  and  cannot  be  separated  by  fractional 
distillation.  Meta  xylene  is  present  in  the  largest  amount  and 
is  of  technical  importance.  It  can  be  separated  from  the 
others  by  boiling  the  mixture  with  dilute  nitric  acid,  which 
oxidizes  the  ortho  and  para  xylenes  into  toluic  acids  while  it 
has  little  effect  on  the  meta  compound.  Also  when  the  mix- 
ture of  xylenes  is  shaken  with  ordinary  sulphuric  acid,  the 
ortho  and  meta  xylenes  are  converted  into  sulphonic  acids 
from  which  the  para  xylene  can  readily  be  separated;  and 


278  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

then  the  sodium  salts  of  the  sulphonic  acids  may  be  more  or 
less  completely  separated  by  crystallization  and  the  ortho 
and  meta  xylenes  recovered  from  them  in  comparative  purity. 
The  distillate  from  coal  tar,  boiling  between  140°-!  70°, 
known  as  "solvent  naphtha,"  is  chiefly  a  mixture  of  the  three  xy- 
lenes with  pseudocumene  and  mesitylene.  It  is  largely  used  as  a 
solvent  of  caoutchouc  in  the  waterproofing  of  fabrics. 

Mesitylene,  trimethylbenzene,  C6H3(CH3)3(i,  3,  5)  is  the  most 
important  of  the  eight  hydrocarbons  of  the  formula  CgH^,  which 
include  three  trimethylbenzenes,  three  methylethylbenzenes, 
and  two  (n-  and  iso-)  propylbenzenes.  It  is  a  product  of  the  "  con- 
densation "  of  acetone,  which  occurs  when  a  mixture  of  acetone  and 
concentrated  sulphuric  acid  is  distilled: 

CH3  CH3 

I  C 

CO  /\ 

/  HC      CH 

HCH2       H2CH       =  |  +3H20 

CH3C        CCH3 

CH3.CO          OC.CH3  \/ 

\  HC 

CHH2  Mesitylene 

Acetone 

This  synthesis  indicates  that  the  structure  of  mesitylene  is 
probably  symmetrical  (1,3,5),  an<^  tm"s  nas  been  proved  to  be  the 
case  by  other  evidence  (cf.  p.  280).  Its  name  was  suggested 
by  the  symmetrical  distribution  of  the  methyl  groups. 

Durene,  tetramethylbenzene,  CioHi4  was  given  its  name  because 
it  is  solid  at  ordinary  temperatures,  a  property  unusual  in  the  aro- 
matic hydrocarbons  up  to  CnHie. 

Cymene,  CioHi4,  p-methyl-iso-propylbenzene,  occurs  in  a  num- 
ber of  natural  oils,  and  is  named  from  cuminium  cyminum,  which 
yields'  Roman  caraway  oil.  This  oil  also  contains  an  aldehyde 
from  which  cumene  (iso-propylbenzene),  CeH5.CH(CH3)2, may  be 
prepared.  Cymene  is  closely  related  to  the  terpenes, 


AROMATIC  HYDROCARBONS  279 

which  are  constituents  of  turpentine,  and  can  be  obtained  from 
them.  It  is  most  readily  prepared  by  treating  camphor,  Ci0Hi6O, 
with  phosphorus  pentoxide,  which  withdraws  the  elements  of 
water. 

Aromatic  Hydrocarbons  With  Unsaturated  Side  Chains 

Closely  allied  to  the  homologues  of  benzene  are  the  hydrocar- 
bons which  contain  unsaturated  aliphatic  radicals  united  tophenyl. 
They,  too,  show  the  characteristic  reactions  of  their  component 
radicals,  and  may  be  regarded  as  substituted  defines  or  acetylenes 
as  well  as  benzene  derivatives.  Two  compounds  typical  of  this 
group  are: 

Styrene,  or  Styrolene,  C6H5.CH:CH2,  which  is  also  vinyl- 
benzene  or  phenyl-ethylene,  was  first  obtained  from  the  resin  storax, 
and  was  named  from  this.  It  is  present  in  coal  tar,  and  is  formed 
when  a  mixture  of  benzene  vapor  and  ethylene  is  led  through  a  red 
hot  tube.  Styrene  may  also  be  made  from  ethylbenzene  by  the 
same  reactions  which  serve  for  the  formation  of  ethylene  from 
ethane  (p.  45).  It  is  best  prepared  from  cinnamic  acid  (p.  357) 
by  distilling  the  acid  alone  or  with  sodium  hydroxide: 

C6H5.CH:CH.CO.OH  =  C6H5.CH:CH2  +  CO2 


Styrene  is  a  liquid  which  boils  at  146°.  It  polymerizes  to 
(CgHs)*  on  heating  to  200°  in  a  sealed  tube,  or  by  treatment  with 
concentrated  sulphuric  acid.  The  same  change  occurs  slowly  on 
standing. 

Phenyl-acetylene,  C6H5.C:CH,  may  be  made  from  phenyl- 
propiolic  acid,  CeHs.CiC.CO.OH,  which  is  obtained  from  cin- 
namic acid  C6H5.CH:CH.CO.OH  by  the  usual  reactions  em- 
ployed to  change  a  double  to  a  triple  bond.  When  phenyl- 
propiolic  acid  is  heated  with  water  to  1  20°,  carbon  dioxide  is 
evolved  and  the  hydrocarbon  is  formed.  It  may  also  be  made 
from  aceto-phenone,  C6H5.CO.CH3,  by  replacement  of  its  oxygen 


280  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

with  chlorine  (by  phosporus  pentachloride)  and  heating  the  aceto- 
phenone  chloride  with  alcoholic  potash: 

2KOH  =  C6H5.CjCH  +  2KC1  +  2H2O 


Phenylacetylene  boils  at  142°  and  gives  the  usual  acetylene 
reactions. 

Orientation 

The  determination  of  the  relative  positions  of  substituents  in 
the  benzene  ring  is  called  "  orientation."  In  the  case  of  a  given 
compound  this  is  accomplished,  in  practice,  by  converting  the 
compound  into  another  in  which  the  positions  are  known.  This 
method,  of  course,  assumes  that  the  new  substituents  which  are 
introduced  in  place  of  the  original  ones  occupy  the  same  positions, 
and  this  is  found  to  be  generally  true. 

The  establishment  of  reference  compounds  has  been  effected 
by  various  methods.  The  synthesis  of  mesitylene  from  acetone 
was  taken  as  presumptive  evidence  that  this  hydrocarbon  is  sym- 
metrical (i,  3,  5)  trimethylbenzene  and  this  structure  has  been 
proved  by  various  replacements  which  show  that  the  three  un- 
substituted  hydrogen  atoms  (2,  4,  6)  are  of  equal  value,  i.e.,  each 
stands  in  the  same  relation  to  the  three  methyl  groups. 


Mesitylene  and  some  of  its  derivatives  may  therefore  serve  as 
reference  compounds. 

A  more  general  principle  is  that  of  Korner.  By  this  it  is  possi- 
ble to  find  whether  a  compound  containing  two  substituents  of 
the  same  kind  is  an  ortho,  meta,  or  para  compound  The  method 
consists  in  determining  the  number  of  trisubstitution  products 


AROMATIC  HYDROCARBONS  281 

which  can  be  made  from  each.  For,  if  another  group  is  introduced 
into  an  ortho  compound,  only  two  isomers  can  be  formed,  since 
position  6  would  give  a  compound  identical  with  position  3  ;  and 
4  and  5  bear  the  same  relation  to  the  original  groups. 

CH3  CH3  CH 

|CH3 


N02 

NO2 

From  a  meta  compound  three  and  only  three  isomers  are  possi- 
ble by  the  introduction  of  a  new  group,  4  and  6  being  identical. 

CH3  CH3  CH3  CH3 

ICH, 


Finally,  a  para  compound  can  give  only  one  product  by  the 
introduction  of  a  new  group,  as  it  is  easily  seen  that  in  the  posi- 
tions 2,  3,  5  and  6,  the  relations  would  be  the  same. 


The  three  xylenes  whose  formulas  have  been  taken  to  illustrate 
this  "absolute"  method  of  orientation,  may  be  converted  into 
the  three  corresponding  dibasic  acids — the  phthalic  acids — whose 
structure  thus  becomes  known,  and  the  positions  of  the  sub- 
stituents  in  other  compounds  can  be  ascertained  by  converting 
them  into  xylenes  or  phthalic  acids,  or  into  other  compounds 


282  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

whose  structure  has  already  been  determined  by  these  or  similar 
conversions. 

Other  Aromatic  Hydrocarbons 

Besides  the  hydrocarbons  of  the  types  already  discussed,  there 
are  many  others  belonging  to  the  aromatic  group,which  contain 
two  or  more  cyclic  radicals.  These  may  be  grouped  as  follows: 
i.  Hydrocarbons  which  may  be  regarded  as  aliphatic  hydro- 
carbons (saturated  or  unsaturated)  in  which  two  or  more  hydro- 
gen atoms  are  replaced  by  phenyl,  such  as  triphenylmethane, 
(C6H5)3CH,  tetraphenylethane,  (C6H5)2CH.CH(C6H5)2,  and  di- 
phenyl  ethylene,  CeHs.CHiCH.CeHs.  2.  Hydrocarbons  which 
consist  of  a  chain  of  cyclic  and  aliphatic  radicals,  such  as  dibenzyl 
benzene,  CeHs.C^.CeH^CH^.CeHs.  3.  Hydrocarbons  formed  by 
the  union  of  phenyl  with  cyclic  radicals,  such  as  phenyl trimethylene, 

/CH2 
C6H5.CHc          ,    diphenyl,    Ce^.CeHs    and  triphenylbenzene, 

^CH2 

C6H3(C6H5)3.  4.  Hydrocarbons  which  contain  "condensed" 
benzene  rings,  with  carbon  atoms  common  to  the  adjacent 
rings.  Examples  of  these  are: 


Naphthalene,  Ci0H8, 
and  Anthracene,  CuHio, 


Finally,  in  many  instances,  two,  four,  or  a  larger  even  number 
of  hydrogen  atoms  can  be  added  to  usual  aromatic  hydrocarbons, 
forming  hydro-aromatic  hydrocarbons,  such  as  dihydro-,  tetra- 
hydro-,  and  hexahydro-benzene.  The  last  named  compound  is 
also  called  hexamethylene,  and  was  mentioned  with  the  cyclo- 
paraffins  (p.  257). 


AROMATIC   HYDROCARBONS  283 

The  possibilities  of  substitution  of  the  hydrogen  in  both  the 
cyclic  and  aliphatic  radicals  of  these  numerous  hydrocarbons 
opens  the  way  for  the  existence  and  production  of  an  immense 
number  of  aromatic  derivatives.  As  has  already  been  stated,  the 
aromatic  compounds  now  known  far  outnumber  those  of  the  ali- 
phatic group,  and  new  ones  are  all  the  time  being  made. 

We  shall  study  here  only  a  very  few  of  these  compounds,  with 
the  purpose  of  becoming  acquainted  with  the  characteristics  of 
the  most  important  types,  and  learning  something  of  their  practi- 
cal relations;  and  shall  discuss  first  the  derivatives  of  those  com- 
pounds which  contain  a  single  cyclic  radical. 


CHAPTER  XXI 

HALOGEN  DERIVATIVES;  SULPHONIC  ACIDS; 
NITRO  COMPOUNDS 

The  three  classes  of  aromatic  derivatives  which  are  the  subject 
of  this  chapter  are  produced  by  the  direct  action  of  the  halogens, 
or  of  sulphuric  or  nitric  acid  on  the  hydrocarbons.  These  com- 
pounds can  also  be  made  by  indirect  methods,  but  except  in 
the  case  of  the  halogen  derivatives  these  methods  are  of  minor 
importance. 

Halogen  Derivatives 

Preparation. — Chlorine  and  bromine  act  on  benzene  under 
ordinary  conditions  slowly,  and  the  replacement  of  the  hydrogen 
is  in  no  case  complete.  The  reaction  proceeds  much  more  read- 
ily, however,  in  the  presence  of  certain  substances,  such  as  iodine, 
iron,  sulphur,  or  chlorides  of  aluminium,  antimony,  or  iron,  which 
are  known  as  "  halogen  carriers  " ;  and  in  this  way  all  the  hydrogen 
atoms  may  be  successively  replaced  with  the  formation,  finally, 
of  CeCleandCeBre. 

When  chlorine  or  bromine  act  without  carriers,  but  in  direct 
sunlight,  the  halogen  adds  itself  to  benzene,  producing  the  final 
products,  C6H6C16  or  C6H6Br6. 

Iodine  does  not  act  directly  on  benzene,  but  iodine  substitution 
products  are  formed  when  some  substance  is  present  to  oxi- 
dize the  hydriodic  acid  formed  in  such  a  reaction.  Such  sub- 
stances are  iodic  acid,  mercuric  oxide,  etc.  Iodine  is,  however, 
introduced  more  conveniently  by  the  diazo-reaction  (cf.  p.  316). 

In  the  case  of  the  homologues  of  benzene,  two  classes  of  halogen 
derivatives  may  be  obtained:  those  in  which  the  substitution  is  in 

284 


HALOGEN  DERIVATIVES  285 

the  cyclic  radical  or"  benzene  nucleus,"  and  those  where  it  is  in  the 
alkyl  group.  When  chlorine  or  bromine  acts  on  the  hydrocarbons 
in  sunlight  or  at  their  boiling  temperature  (in  the  absence  of  a 
carrier)  substitution  takes  place  chiefly  in  the  side  chains;  but  in 
the  dark  and  at  ordinary  temperatures,  it  is  the  hydrogen  of  the 
cyclic  group  which  is  replaced.  The  latter  reaction  occurs  more 
readily  in  the  homologues  of  benzene  than  in  benzene  itself,  on 
account  of  the  presence  of  the  positive  alkyl  group,  but  is  pro- 
moted by  the  addition  of  a  catalyst. 

Both  classes  of  halogen  compounds  may  be  made  from  the  cor- 
responding hydroxyl  compounds  by  means  of  the  phosphorus 
halides.  When  the  hydroxyl  group  is  in  the  side  chain,  this  reac- 
tion generally  takes  place  readily,  as  in  the  case  of  the  aliphatic 
hydroxyl  compounds,  but  hydroxyl  in  the  cyclic  radical  is  less  eas- 
ily replaced.  Halogens  may  also  be  introduced  into  side  chains 
by  the  addition  of  the  halogen  or  hydrogen  halide  to  unsaturated 
side  chains,  as  in  the  aliphatic  series. 

Halogen  substituted  hydrocarbons  with  the  halogen  in  the 
nucleus  can  also  be  obtained  indirectly  by  distilling  halogen  sub- 
stituted acids  with  lime,  as  in  the  formation  of  hydrocarbons  from 
acids: 

C6H4Br.CO.OH  +  CaO  =  CeHsBr  +  CaCO3 

A  most  important  general  method  for  the  preparation  of  halogen 
derivatives,  containing  the  halogen  in  the  nucleus,  depends  on  the 
ready  formation  and  decomposition  of  diazo  compounds  (p.  316), 
and  will  be  discussed  later.  Starting  with  the  hydrocarbon,  the 
steps  are  the  following, 


/CH3  /CH3  /CH3 

C6K5.CH3 >  CeH/         ->  C6H4<  -»  C6H4< 

XNO2  XNH2  xN:NBr 

Toluene  Nitrotoluene  Toluidine  Diazo  compound 

XCH3 
C6H4/         . 
XBr 

Bromtoluene 


286 


INTRODUCTION  TO   ORGANIC   CHEMISTRY 


When  two  chlorine  or  bromine  atoms  are  substituted  in  the 
benzene  nucleus  by  direct  reaction  on  benzene,  the  chief  product  is 
the  para  compound,  a  small  amount  of  ortho  compound  being 
formed  at  the  same  time.  Similarly,  when  mono-chlor  or  brom- 
toluene  is  made  by  direct  substitution,  the  product  is  mainly  the 
para  compound  with  a  little  of  the  ortho  derivative.  The  influ- 
ence of  groups  already  present  on  the  entrance  of  other  substitu- 
ents,  and  how  these  may  be  directed  to  certain  positions  will 
be  taken  up  later  (p.  298).  In  the  preparation  of  the  halogen 
derivatives  by  the  direct  action  of  the  halogen,  the  theoretical 
amount  of  the  halogen  necessary  to  give  the  special  derivative,  or 
a  slight  excess  of  it,  is  added.  Bromine  is  weighed  directly  before 
adding  it,  but  the  weight  of  chlorine  is  usually  determined  by 
noting  the  increase  in  the  weight  of  the  flask  in  which  the  reaction 
takes  place. 

SOME  TYPICAL  HALOGEN  COMPOUNDS 

Name 


Chlorbenzene,  Phenyl 

chloride 

Hexachlorbenzene 
Brombenzene 
o-Dibrombenzene 
m-Dibrombenzene 
p-Dibrombenzene 
Adj-Tribrombenzene 
Unsym-Tribrombenzene 
Sym-tribrombenzene 
lodobenzene 
p-Di-iodobenzene 
o-Chlortoluene 
p-Chlortoluene 
Benzylchloride,    Chlor- 

methylbenzene 
Benzalchloride,  Dichlor- 

methylbenzene 
Phenylchloroform,  Tri- 

chlormethylbenzene 


Formula 
CeHsCl 

C6H6Br 
C6H4Br2  (i,  : 
C6H4Br2  (i,  - 
C6H4Br2  (i,  < 
C6H3Br3  (i,  : 
C6H3Br3  (i,  : 
C6H3Brs  (i,  •. 
C6H6I 

:,4) 


C6H4C1.CH3 


C6H6.CH2C1 
C6H6.CH.C12 


C6H6CC13 


Melting 
point 

-44-9° 
227 

Boiling 
point 

132° 
326° 

f           Specific 
gravity 

I.I06   (20°/4°) 

-30.5 

—    I 
+    1-2 

89-3 
)            87 

157 
224 
22O 
2I9 

1.491  (20°/4°) 
2.003  (o°) 

1.955(19°) 
1.841  (89°) 

)         44 

\       1  20 

278 

-28.5 

1  88 
28* 

1.861  (o°) 

2)  —  ^ 

4)          74- 

162 

-43-2 
-16.1 

179 
204 

1.113(15°) 

1.295  (16°) 

—  22.5  213-214  1.38  (14°) 


HALOGEN  DERIVATIVES  287 

Properties  and  Reactions.  —  Some  of  the  halogen  derivatives  are 
liquids,  but  most  of  them  are  solids.  They  are  readily  soluble  in 
alcohol,  ether,  etc.,  but  are  usually  insoluble  or  only  slightly  sol- 
uble in  water.  The  compounds  containing  a  halogen  in  the  side 
chain  generally  have  a  pungent  and  irritating  odor,  while  those  in 
which  the  halogen  is  in  the  nucleus  have  a  much  weaker  and  not 
unpleasant  smell.  Like  all  other  organic  halogen  derivatives  they 
are  less  inflammable  than  the  corresponding  hydrocarbons. 

When  the  halogen  is  in  the  nucleus,  it  is  held,  as  a  rule,  so  firmly 
that  it  does  not  readily  enter  into  reaction.  Compounds  of  this 
kind  may  be  boiled  with  alkalies,  silver  hydroxide,  ammonia, 
potassium  cyanide,  or  acid  sulphites  without  being  sensibly 
affected.  But  the  halogen  atom  shows  a  greater  reactivity  when 
certain  other  substituents  are  present  —  for  instance,  o-  and  p- 
nitrochlorbenzene,  C6H4C1.NO2,  give  with  alcoholic  potash  the 
corresponding  nitrophenols,  C6H4(OH)NO2.  Sodium,  however, 
removes  the  halogen,  and  usually  at  ordinary  temperatures 
(Fittig's  reaction,  p.  273),  e.g.,  the  syntheses  of  diphenyl  and 
toluene: 


2C6H6Br  +  2Na  =  C6H5.C6H5  +  2NaBr 

Diphenyl 

C6H5Br  +  CH3Br  +  2Na  =  CeH^CHa  +  2NaBr 


Magnesium  also  reacts  with  the  halogen  compounds  as  de- 
scribed under  Grignard's  synthesis  (p.  36). 

When  the  halogen  is  in  the  side  chain  it  is  readily  replaced  by 
the  hydroxyl,  amino,  cyanogen,  and  other  groups  by  the  reactions 
employed  with  aliphatic  halogen  compounds.  Thus  benzyl- 
chloride,  C6H5.CH2C1,  may  be  converted  into  benzylalcohol, 
C6H5>CH2OH,  benzylamine,  C6H5.CH2NH2,  or  benzylcyanide, 
CcHs.CH^CN,  by  the  action  of  water  or  alkalies,  ammonia,  or 
potassium  cyanide,  as  in  the  case  of  the  aliphatic  halides. 

This  difference  in  reactivity  according  to  the  place  occupied  by 
the  halogen  may  frequently  be  made  the  basis  for  determining 
whether  the  halogen  is  in  the  ring  or  in  the  side  chain.  If  the 


288  INTRODUCTION   TO  "  ORGANIC   CHEMISTRY 

substance  is  boiled  with  alcoholic  potash  and  the  solution  is  then 
acidified  with  nitric  acid  and  tested  with  silver  nitrate,  a  precipi- 
tate of  silver  halide  shows  that  the  halogen  has  been  displaced 
from  the  organic  compound  and  hence  was  probably  present  in 
the  side  chain;  while  no  precipitation  indicates  that  the  halogen 
was  in  the  ring. 

Benzalchloride,  CeHB.CHC^,  and  benzotrichloride  (phenyl- 
chloroform),  C6H5.CC13,  are  made  commercially  by  the  action 
of  chlorine  on  toluene,  and  are  employed  in  the  preparation  of 
benzaldehyde,  C6H5.CHO,  and  benzoic  acid,  C6H5.CO.OH, 
respectively. 

Sulphonic  Acids 

The  action  of  sulphuric  acid  on  aromatic  compounds  is  one  of 
the  most  striking  characteristics  of  this  group  of  compounds. 
All  aromatic  compounds  dissolve  in  concentrated  or  fuming  sul- 
phuric acid  with  greater  or  less  readiness,  and  from  these  solutions 
compounds  are  obtained  in  which  hydrogen  of  the  nucleus  is 
found  to  be  replaced  by  the  sulphonic  acid  group,  —  S03H: 

C6H5.CH3  +  H2SO4  =  CH3.C6H4S03H  +  H2O 

Toluene  Toluenesulphonic  acid 

Aliphatic  compounds  react  with  sulphuric  acid  much  less 
readily;  and  prolonged  heating  results  in  only  a  partial  and  un- 
satisfactory production  of  sulphonic  acids  (p.  241). 

Aromatic  sulphonic  acids  may  also  be  made,  as  the  aliphatic 
sulphonic  acids  are,  by  the  oxidation  of  the  corresponding  sulph- 
hydrogen  compounds  (thiophenols),  and  the  sulphonic  acid  group 
may  be  introduced  by  other  methods;  but  the  preparation  of  the 
sulphonic  acids  is  almost  aways  effected  by  the  direct  action  of 
sulphuric  acid.  The  ease  with  which  this  reaction  proceeds  is 
markedly  influenced  by  the  presence  of  other  substituting  groups. 
In  general,  alkyl  or  other  positive  groups  favor  the  reaction,  while 
carboxyl  and  other  acid  groups  render  it  more  difficult;  and  the 


SULPHONIC   ACIDS  289 

successive  replacement  of  hydrogen  atoms  by  the  sulphonic  acid 
group  becomes  impossible  after  three  such  groups  have  been 
introduced.  The  process  of  making  sulphonic  acids  is  called 
sulphonation. 

Preparation. — In  the  preparation  of  sulphonic  acids  the  aro- 
matic hydrocarbon  or  other  compound  is  boiled  for  some  time  with 
concentrated  sulphuric  acid,  or  gently  heated  for  a  shorter  time 
with  fuming  acid,  and  then  the  mixture  of  sulphonic  acid  with  the 
excess  of  sulphuric  acid  is  poured  into  water.  The  sulphonic  acids 
of  the  hydrocarbons  are  mostly  very  soluble  in  water  and  may  be 
separated  from  sulphuric  acid  in  the  following  way:  By  neu- 
tralizing the  mixture  with  carbonate  of  calcium,  barium  or  lead, 
the  sulphuric  acid  is  precipitated  as  an  insoluble  sulphate,  while 
the  calcium,  barium,  or  lead  salt  of  the  sulphonic  acid  remains  in 
solution,  and  may  be  obtained  by  evaporation  or  converted  into 
other  salts  by  double  decomposition,  as,  for  instance,  into  the 
sodium  salt  by  adding  sodium  carbonate.  The  free  acid  may  be 
obtained  from  the  calcium  or  barium  salt  by  exact  precipitation 
with  sulphuric  acid,  or  from  the  lead  salt  by  decomposition  with 
hydrogen  sulphide.  Another  method  depends  on  the  fact  that 
many  of  the  sodium  salts  are  difficultly  soluble  in  a  solution  of 
sodium  chloride,  and  hence  are  precipitated  when  the  product 
of  the  reaction  is  poured  into  a  saturated  solution  of  common 
salt — a  result  of  the  changed  ionic  concentration. 

The  sulphonic  acids  of  some  aromatic  compounds  are  precipi- 
tated by  ice-water  and,  in  a  number  of  cases,  by  concentrated 
hydrochloric  acid. 

Properties. — 'Aromatic  sulphonic  acids  are  solids  which  crystal- 
lize from  water,  in  which  many  of  them  are  very  soluble.  The 
sulphonic  acid  salts  are  also  mostly  soluble  in  water  and  many  of 
them  crystallize  well. 

Reactions. — i.  The  sulphonic  acids  are  strong  acids,  forming 
salts  by  the  replacement  of  the  hydrogen  of  the  —  SOsH  group  by 
metals;  and  esters,  such  as  C6H6.S03C2H5,  with  alcohols. 


2  90  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

2.  Phosphorus  pentachloride  converts  the  sulphonic  acids  or 
their  salts  into  sulphonic  acid  chlorides: 

CeHe.SOaH  +  PC15  =  C«H6.SO2C1  +  POC13  +  HC1 

3.  Melted  with  alkalies,  the  alkali  salts  of  sulphonic  acids  have 
their  sulphonic  acid  group  replaced  by  hydroxyl: 

C6H6.S03Na  +  NaOH  =  C6H6.OH  +  Na2SO3 

Phenol 

This  reaction  serves  as  the  best  practical  method  for  making 
certain  commercial  phenols  such  as,  resorcinol,  C6H4(HO)2, 
naphthol,  CioH7.OH,  alizarin,  Ci4H6O2(OH)2,  etc. 

4.  Melted  with  potassium  cyanide,  the  alkali  salts  give  aromatic 
cyanides  (nitriles)  which  may  be  hydrolyzed  to  acids: 

C6H5.S03K  +  KCN  =  CeHs.CN  +  K2SO3 

5.  Melted  with  sodium  formate,  the  alkali  salts  form  salts  of 
carboxyl  acids, 

CeHe.SOaNa  +  HCO.ONa  =  C6H6.CO.ONa  +  NaHSO3 

Sodium  benzoate 

6.  Heated  with  sodium  amide,  the  alkali  salts  give  aromatic 
amines: 


OaNa  +  NaNH2  =  CeHs-NI^  +  Na2SO3 

Aniline 

7.  The  sulphonic  group  is  replaced  by  the  nitro  group  in  some 
sulphonic  acids  by  treatment  with  strong  nitric  acid. 

8.  The  sulphonic  acid  group  is  replaced  by  hydrogen  by  dis- 
tillation of  the  acid,  or  most  effectively  by  means  of  steam  under 
pressure: 

CH3.C6H4.SO3H  +  H20  =  CH3.C6H5  +  H2SO4 

Toluenesulphonic  acid  Toluene 

This  reaction  following  the  sulphonation.  of  a  mixture  of  hydro- 
carbons and  separation  of  the  sulphonic  acids  is  sometimes  used  for 
the  preparation  of  pure  hydrocarbons;  for  the  sulphonic  acids  can 
be  separated  by  crystallization  more  readily  and  completely  than 
the  hydrocarbons  by  distillation. 


SULPHONIC  ACIDS  2QI 

9.  Sulphonic  acid  chlorides  react:  (a)  Slowly  with  water  or 
alkalies,  forming  the  sulphonic  acid  or  its  salts,  (b)  With  am- 
monia or  primary  or  secondary  amines  with  the  formation  of  sim- 
ple or  substituted  acid  amides: 


OsCl  +  CH3NH2  =  C6H5.SO2.NH.CH3  +  HC1 

(c)  With  alcohols,  the  chlorides  give  sulphonic  acid  esters: 
C6H5.SO2C1  +  C2H6OH  =  C6H6.S02.OC2H6  +  HC1 

(d)  Nascent  hydrogen  reduces  the  chlorides  to   thiophenols, 
e.g.,  CeHe.SH. 

(e)  When  distilled  with  phosphorus  pentachloride  the  sulphonic 
acid  group  is  replaced  by  chlorine. 

The  structure  of  the  aromatic  sulphonic  acids  is  inferred  from 
the  reactions  common  to  these  compounds  and  the  sulphonic 
acids  of  the  aliphatic  series  (p.  241).  The  reaction  with  phos- 
phorus pentachloride  shows  the  presence  of  the  hydroxyl  group, 
and  the  reduction  of  the  acid  chloride  to  a  thiohydride  proves  that 
the  sulphur  atom  is  united  directly  to  nucleus  carbon.  The 


structure   is   therefore   R  -  S02. OH  and  probably  R  -  S^=  O    . 

\OH 

The  sulphonic  acids  may  thus  be  regarded  as  sulphuric  acid  in 
which  one  hydroxyl  has  been  replaced  by  an  aromatic  radical. 

Uses. — On  account  of  the  many  reactions  which  they  give,  and 
their  own  ready  preparation,  the  sulphonic  acids  are  largely 
employed  in  chemical  work.  Sulphonation  serves  also  to  bring 
insoluble  substances  into  a  soluble  condition,  so  that  insoluble 
dyes,  for  instance,  which  cannot  be  directly  employed  on  account 
of  their  insolubility,  are  made  available  for  dyeing  in  the  form  of 
their  sulphonic  acids.  Further,  the  sulphonic  acid  salts,  the  acid 
chlorides,  and  amides  are  used  for  the  identification  of  aromatic 


2Q  2  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

hydrocarbons.  The  amides  are  especially  good  for  this  purpose, 
since  they  crystallize  well  from  hot  water  and  have  well-defined 
melting  points.  Benzenesulphonyl  chloride,  CeEU.SC^C^maybe 
used  to  distinguish  the  three  classes  of  amines.  It  does  not  react 
with  tertiary  amines;  but  with  primary  and  secondary  amines 
forms  substituted  acid  amides  which  are  distinguished  by  the  fact 
that  the  product  from  the  primary  amine  is  soluble  in  sodium 
hydroxide,  while  that  from  the  secondary  amine  is  insoluble. 
This  difference  in  solubility  is  due  to  the  presence  in  the  former 
compound  of  hydrogen  which  is  replaced  with  sodium  by  the 
action  of  sodium  hydroxide: 

C6H5.SO2NH.CH3  +  NaOH  -^CeHs.SOaNNa.CHa 

while  in  the  secondary  product  there  is  no  replaceable  hydrogen  in 
the  acid  amido  group  :  C6HB.SO2N(CH3)2. 

In  the  following  table  are  given  a  few  typical  sulphonic  acids 
with  the  melting  points  of  their  chlorides  and  amides.     "  Sulph- 
onic acid"  is  to  be  added  in  each  case  to  the  name  which  is  given. 
SULPHONIC  ACIDS 

Melting  Points 

Name  Formula  Chlorides  Amides 

Benzene  C6H6.SO2OH  14  -5°         *S°0 

m-Benzenedi-  C6H4.(SO2OH)2  (i,  3)  63  229 

p-Benzenedi-  C6H4.(SO2OH)2  (i,  4)  131 

Benzenetri-  C6H3(SO2OH)3  (i,  3,  s)  l84  306 


o-Toluene-  CeH  (i.  2)          liquid  153 

SO2OH 


p-Toluene-  C6H  (i,  4)  96 

XS02OH  136 

/CHa  (i) 

o-Xylene-  C6H3.CH8  (2)  51-52  144 

\S02OH  (4) 


NITRO    COMPOUNDS  293 

A  substance  may  be  identified  as  a  sulphonic  acid  or  a  sulphonic- 
acid  salt  by  fusing  it  with  sodium  hydroxide  and  treating  the 
product  with  water  and  a  dilute  acid.  If  the  sulphonic-acid  group 
is  present,  sulphur  dioxide  is  evolved,  and  a  phenol  remains  in 
solution  which  is  detected  by  adding  ferric  chloride,  or  bromine 
water  (cf.  p.  330). 

Compounds  containing  the  sulphonic  group  in  the  side  chains  of 
aromatic  compounds  may  be  made  by  the  methods  given  for 
forming  the  alkyl-sulphonic  acids  (p.  241). 

Nitro  Compounds 

The  action  of  nitric  acid  on  aromatic  hydrocarbons  has  already 
been  noted.  The  dilute  acid  when  heated  with  homologues  of 
benzene  usually  oxidizes  one  or  more  of  the  side  chains  to  the 
carboxyl  group.  Occasionally,  under  certain  conditions,  hydro- 
gen of  the  alkyl  groups  is  replaced  by  the  nitro  group,  NO2, 
producing  such  compounds  as  CeHs.CH^.NC^;  and  usually  small 
amounts  of  compounds  are  produced  which  contain  the  nitro 
group  in  place  of  nucleus  hydrogen.  With  concentrated  nitric 
acid  this  last  reaction  becomes  the  chief  one;  one,  two,  or  three 
nitro  groups  being  introduced  into  the  aryl  radical.  This  reaction 
is  called  nitration,  and  the  resulting  substances  are  nitro  com- 
pounds: 


C6H5.CH3  +  HNO3  =  C6H4(CH3)NO2  +  H2O 

Toluene  Nitrotoluene 

In  nitrating  the  homologues  and  other  derivatives  of  benzene, 
the  ease  of  the  reaction  is,  of  course,  influenced  by  the  character  of 
the  groups  which  are  present-  and  since  the  nitro  group  is  a 
strongly  acid  group,  the  statements  made  in  regard  to  sulphona- 
tion  (p.  288),  apply  in  general  to  nitration.  It  has  proved  impos- 
sible to  introduce  in  this  way  more  than  three  nitro  groups  into  a 
compound.  In  many  cases,  fuming  nitric  acid  is  necessary  to 
effect  nitration,  and  very  commonly  a  mixture  of  concentrated  or 


2Q4  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

fuming  nitric  acid  with  sulphuric  acid  is  used,  the  sulphuric  acid 
uniting  with  the  water  formed  in  the  reaction  and  thus  preventing 
the  dilution  of  the  nitric  acid.  On  the  other  hand,  some  sub- 
stances are  readily  nitrated  by  dilute  acid.  Phenol,  for  instance, 
can  be  nitrated  by  a  mixture  of  concentrated  nitric  acid  with  twice 
its  volume  of  water.  The  number  of  nitro  groups  introduced 
depends  in  each  case  upon  the  strength  of  the  acid,  the  tempera- 
ture, and  the  nature  of  the  aromatic  compound.  Nitrobenzene, 
C6H5.NO2,  is  manufactured  in  large  quantities  by  allowing  a  mix- 
ture of  concentrated  nitric  and  sulphurjc  acids  to  flow  into  ben- 
zene which  is  continually  stirred  and  cooled.  Dinitrobenzene, 
C6H4(NO2)2,  results  if  the  mixture  is  not  cooled  but  allowed  to 
heat  from  the  effect  of  the  reaction;  while  the  formation  of 
trinitrobenzene,  C6H3(NO2)3,  requires  fuming  acid  and  a  higher 
temperature  (180°).  In  general,  it  is  advantageous  to  carry 
on  the  nitration  at  as  low  a  temperature  as  is  effective,  espe- 
cially when  the  compounds  contain  groups  subject  to  oxidation. 

Nitro  compounds  can  also  be  formed  from  aromatic  amines  by 
oxidation  or  by  the  replacement  of  the  amino  group  by  the  nitro 
group  through  diazo  compounds;  but  these  methods  are  only  of 
theoretical  interest,  practically  all  nitro  compounds  being  pre- 
pared by  direct  nitration,  as  the  sulphonic  acids  are  by  direct 
action  of  sulphuric  acid. 

The  introduction  of  the  nitro  group  into  side  chains  cannot  be 
effected,  as  one  might  expect,  by  the  reaction  between  the  halogen 
compound  and  silver  nitrite  (cf.  p.  142).  But  the  nitration  of 
saturated  side  chains  can  be  accomplished  directly  by  dilute 
nitric  acid  under  certain  conditions.  For  example,  when  ethyl- 
benzene  is  heated  in  a  sealed  tube  with  weak  nitric  acid  (sp.  grav. 
1.076)  to  io5°-io8°,  a  good  yield  of  phenylnitroethane,  C6H6.- 
CHNO2.CH3,  is  obtained.  Nitro  compounds  with  the  nitro 
groups  in  unsaturated  side  chains  may  often  be  made:  i.  by  the 
action  of  nitric  or  nitrous  acid  or  nitrogen  tetroxide  on  the  unsatu- 
rated hydrocarbon.  Styrene,  for  example,  CeEU.CH  :  CH2, 


NITRO    COMPOUNDS  2Q5 

in  ethereal  solution  reacts  with  nitrous  acid  to  form  phenylnitro- 
ethylene,  C6Hs.CH:CHNO2.  2.  Similar  compounds  can  also 
be  made  synthetically  from  nitro  paraffins  and  benzaldehyde, 
,  in  the  presence  of  zinc  chloride: 


ZnCli 

C6H6.CHO  +  CH3NO2  =  C6H5.CH:CHNO2  +  H2O 

ZnCl. 

C6H5.CHO  +  CH3.CH2NO2  =  C6H5.CH:C.NO2  +  H2O 

I 
CH3 

The  compounds  with  nitro  groups  in  side  chains  are,  however, 
of  very  minor  interest,  while  the  importance  of  the  nitro  com- 
pounds containing  the  nitro  groups  in  place  of  nucleus  hydrogen 
can  hardly  be  over-estimated.  Their  importance  lies  chiefly  in 
the  fact  that  these  nitro  compounds  form  the  first  step  in  the  intro- 
duction of  other  groups  into  the  cyclic  radicals,  for  the  nitro 
compounds,  as  such,  find  only  a  limited  use.  In  the  following, 
only  those  compounds  which  have  nitro  groups  in  the  ring  will 
be  considered. 

Properties.  —  The  mononitro  derivatives  of  the  lower  aromatic 
hydrocarbons  are  liquids  or  crystalline  solids  having  an  odor  like 
that  of  bitter-almond  oil.  The  liquid  compounds  are  pale  yellow, 
and  the  solids  yellow  or  colorless.  They  are  heavier  than  water 
and  insoluble  in  it.  They  are  volatile  with  steam  and  can  in 
most  cases  be  distilled  without  decomposition.  Compounds 
with  two  or  three  nitro  groups,  on  the  contrary,  in  most  cases  do 
not  distil  at  ordinary  pressure  without  decomposition,  and  the 
decomposition  is  usually  the  occasion  of  a  more  or  less  violent 
explosion.  They  are,  however,  stable  beyond  their  melting  points, 
and  these  are  often  determined  for  purposes  of  identification. 

Reactions.  —  i.  The  most  important  reaction  of  the  nitro  com- 
pounds is  the  reduction  they  undergo  with  active  reducing  agents, 
with  the  conversion  of  the  nitro  group  into  the  amino  group.  In 
the  laboratory  the  reduction  is  usually  effected  by  means  of  tin 


296  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

and  hydrochloric  acid,  while  iron  filings  and  hydrochloric  acid 
are  commonly  employed  in  technical  operations  (cf.  p.  303). 
Various  other  reducing  agents  may,  however,  be  used: 

C6H5.NO2  +  6H  =  C6H5.NH2  +  2H2O 

Nitrobenzene  Aniline 

The  amines  which  are  products  of  these  reductions  form  the  sec- 
ond step  in  the  introduction  of  various  groups  in  place  of  nucleus 
hydrogen,  the  third  being  the  conversion  of  the  amine  into  a  diazo 
compound  (p.  313). 

2.  By  the  use  of  milder  reducing  agents  several  intermec[iate 
reduction  products  can  be  produced  (p.  321).     All  of  these  sub- 
stances are  converted  into  amines,  e.g.,  aniline,  by  further  reduc- 
tion, and  some  of  them  at  least,  form  transition  steps  in  the  active 
reduction  which  yields  the  amines  directly,  and  are  also  produced 
by  oxidation  of  the  amines. 

3.  The  direct  replacement  of  the  nitro  group  by  other  groups 
cannot  usually  be  effected.     This  is  especially  true  of  the  mono- 
nitro  compounds.     When  two  nitro  groups  are  present  in  the 
ortho  or  para  position  to  each  other,  one  of  them  can  be  exchanged 
for  hydroxyl  by  boiling  with  a  solution  of  sodium  hydroxide;  or 
for  the  amino  group  when  heated  with  an  alcoholic  solution  of 
ammonia.    These  reactions  do  not  occur  when  the  groups  have  the 
meta  positions.    Trinitro  compounds,  however,  give  similar  reac- 
tions whatever  the  positions.     Thus  symmetrical  trinitrobenzene 
(i,  3,  5)  is  converted  slowly  at  ordinary  temperature  by  sodium 
methoxide,  CH3ONa,  into  dinitro  anisol,  C6H3(NO)2(O.CH3). 

4.  The  influence  of  the  presence  of  the  nitro  group  is  seen  in 
many  reactions,  and  we  may  note  here  that  hydrogen  situated 
in  the  ring  between  nitro  groups  is  rendered  more  active,  so  that, 
for  instance,  symmetrical  trinitrobenzene  is  oxidized  by  potassium 
ferricyanide  to  trinitrophenol,  CgHWOHXNC^a. 

Structure  of  Nitro  Compounds. — Two  facts  indicate  that  the 
nitro  group  is  —  NOg  and  not  the  nitrous  acid  radical  —  ONO. 


NITRO    COMPOUNDS 


2Q7 


These  are:  i.  That  the  mononitro  compounds  cannot  be  saponi- 
fied as  a  nitrous  ester  would  be,  and  2.  The  reduction  of  the  group 
to  an  amino  group,  instead  of  to  hydroxyl,  which  would  be  the 
probable  result  if  the  compound  had  the  ester  formation.  Hence 
the  nitrogen  of  the  nitro  group  is  directly  united  to  the  ring  car- 
bon, and  the  structure  is 


NITRO  COMPOUNDS 

Name 

Formula 

Melting 
point 

Boiling 
point 

Specific 
gravity 

Nitrobenzene 
o-Dinitrobenzene 
m-Dinitrobenzene 
p-Dinitrobenzene 
unsym.-trinitrobenzene 
sytn-trinitrobenzene 

o-nitrotoluene 

C6H6.NO2 

C6H4(N02)2  (i,  2) 
C6H4(N02)2  (i,  3) 
C6H4(N02)2  (i,  4) 
C6H3(N02)3  (i,  2,  4) 
C6H3(N03)3  (i,  3,  5) 

/CH3  (i) 
CeH4\N02  (2) 

5-7° 

"7° 

90° 

172° 
57-5° 

122° 
-13-8° 

210.  9°I. 
319°      -. 

303°      I. 
2OO° 

204  (20°) 
369  (98°) 

222.  3°  I. 

168  (15°) 

m-nitrotoluene 

/CH,(i) 
CeH4\N02  (3) 

16° 

230°         I 

.168  (22) 

p-nitrotoluene 

/CH3  (i) 
CeH4\N02  (4) 

54° 

237.  7°i. 

123  (54°) 

Dinitrotoluene 

/CH3  (i) 

["\(N02)2(2,  4) 

70° 

....       I  ., 

32i  (7o°) 

Trinitrotoluene  (T.N.T.; 

)CeH2/CH3(i) 

82° 

Nitroorthoxylene 


29 


^58°     1.139(30°) 


Dinitrometaxylene 


. 
(2,  4) 


82 


298  INTRODUCTION  TO   ORGANIC  CHEMISTRY 

NITRO  COMPOUNDS     (Continued) 

KT  TO          i  Melting     Boiling  Specific 

Name  Formula  point        point  gravity 

'CH3  (i) 

'N02  (2) 

Trinitrometaxylene      C8H  ^  (—  CH3  (3)  182°         

-N02  (4) 
(6) 

,CH3  (i) 

Nitromesitylene  C6H2<^°*  ^  44°         255°         

3  (5) 


(i) 

Nitrocymene  C6H3f  NO2  (2)  liquid       1.085(15°) 

NCH(CH3)2  (4) 


Nitrobenzene,  CeHs.NC^,  is  technically  the  most  important  of 
the  nitro  compounds  of  the  aromatic  hydrocarbons.  It  was  dis- 
covered by  Mitscherlich,  in  1834.  Its  first  practical  use  was  as  a 
substitute  for  oil  of  bitter  almonds  in  perfumery.  While  it  is 
still  used  to  scent  many  commercial  substances,  this  is  of  quite 
minor  importance  as  compared  with  the  employment  of  nitro- 
benzene for  making  aniline  for  the  manufacture  of  coal  tar  dyes. 

The  Influence  of  Substituents  on  Each  Other 

The  fact  that  the  presence  of  a  substituent  in  the  benzene 
ring  influences  both  the  readiness  with  which  a  second  atom  or 
group  can  be  introduced,  and  the  position  which  it  occupies,  has 
been  noticed.  Sulphonation  and  nitration  proceed  more  easily 
with  compounds  which  contain  alkyl  or  hydroxyl  groups  than  with 
benzene  or  derivatives  in  which  a  nitro  or  sulphonic  group  is 
already  present;  and  not  only  is  the  position  of  the  entering  group 
affected  by  the  character  of  the  group  attached  to  the  nucleus, 
but  also  the  reactivity  of  both  groups  in  the  resulting  compound. 
A  second  nitro  or  sulphonic  group  enters  chiefly  in  the  meta  posi- 


RULES   FOR   SUBSTITUTION  2QQ 

tion  to  the  first,  while  a  second  chlorine  or  bromine  atom  gives 
principally  a  para  compound. 

The  following  rules  are  found  to  be  generally  applicable: 

1.  When  an  alkyl  group,  a  halogen  atom,  or  either  of  the 
groups  NH2  or  OH,  is  present,  a  second  alkyl  group  (by  Friedel 
and  Craft's  synthesis),  halogen  atom,  or  the  sulphonic  or  nitro 
group,  enters  in  the  para  or  ortho  position,  the  chief  product 
being  generally  the  para  compound. 

2.  Compounds  containing  one  of  the  groups,  NC>2,  SOsH,  CN, 
CO.OH,   or   CHO  give  on  a  second  substitution  chiefly  meta 
compounds. 

These  statements  may  conveniently  be  put  in  the  form  of  a 
table,  in  which  the  positions  are  indicated  by  the  conventional 
numbers,  bracketed  numbers  meaning  that  these  compounds  are 
produced  in  relatively  small  amounts. 

Element  or  group  Positions  of  substitutes 

in  position  i  Alkyl  Cl  Br  I  SOsH  NO2 

Alkyl 
Cl 
Br 
I 

OH 
NH2 

S03H  4(2)  ....  3  ....  3(4)  3(2,4) 

N02  4(2)  3  ...  3(2,4)  3(2,4) 

CO.OH  4  (2)  3  3  3  3  (4)  3  (2,  4) 

CN  4  3 

To  the  illustrations  already  given  may  be  added  the  great  readi- 
ness with  which  phenol,  CeHs-OH,  reacts  with  bromine,  giving 
symmetrical  tribromphenol;  and  with  nitric  acid,  with  the  produc- 
tion of  ortho  and  para  nitrophenol,  ortho-para  and  diortho-nitro- 
phenol,  and  para  diorthonitrophenol  (p.  337). 

As  regards  the  activity  of  the  products,  the  meta  compounds,  as 
a  class,  are  more  stable  toward  reagents  than  the  ortho  or  para 


4(2) 
4(2) 
4(2) 

4(2) 
4(2) 

4(2) 
4 
4(2) 

4 

4(2) 
4 
4 

4(2) 
4(2) 
4(2) 
4  (2) 

4(2) 
4(2) 

4(2) 

4 

4(2) 
4 

4(2) 
4 

4(2) 
4 

*T  \  *"  f 

4(2) 
4(2) 

300  INTRODUCTION  TO   ORGANIC  CHEMISTRY 


compounds.  Ortho  and  para  bromnitrobenzene, 
react  with  ammonia  to  form  the  corresponding  nitranilines, 
NH2.CeH4.NO2,  while  meta  bromnitrobenzene,  and  brombenzene 
itself,  are  not  affected  by  ammonia.  Many  further  illustrations  of 
the  reciprocal  influence  of  substituents  on  reactions  will  be  met 
with  in  the  course  of  our  study. 


CHAPTER  XXII 
AROMATIC  AMINES 

All  aromatic  amines  contain,  of  course,  one  or  more  aryl  (or 
substituted  aryl)  radicals.  Considering  them  as  substituted 
ammonias,  we  may  distinguish  the  following  types  of  simple  aro- 
matic amines:  i.  Those  in  which  one  or  more  cyclic  radicals  are 
substituted  for  hydrogen  in  NH3,  nitrogen  being  united  to  nucleus 
carbon.  Of  this  type  are  aniline  CeHsNH^,  triphenylamine 


(C6H5) 8N,  toluidine  C6H4  <          ,  etc. 

XNH2 

2.  Those  in  which  the  nitrogen  of  the  substituted  ammonia  is 
combined  with  carbon  in  a  side  chain,  such  as  CeH5.CH2NH2, 
etc. 

3.  Mixed  amines  which  contain  both  phenyl  and  alkyl  groups 
combined  directly  with  nitrogen   as  in  CeH^.NH.CHs;  phenyl 
and  phenyl-alkyl   groups,  such   as   C6H5.CH2.NH.C6H5;  and, 
finally,  amines  containing  alkyl  and  phenyl-alkyl  groups  such  as 
CeHs-CHij.NH.CHa.  These  mixed  amines  are  necessarily  second- 
ary and  tertiary  amines,  while  all  three  classes,  primary,  second- 
ary, and  tertiary  may  be  represented  in  the  first  two  types. 

4.  Aromatic  amines  containing  two  or  more  amino  groups  are 

,'CH; 
also  known,  and  may  be  of  the  type  of  C6H4(NH2)2, 


etc.,  with  the  amino  groups  all  united  to  nucleus  carbon;  or  such 


as  CeH  ,  with  an  amino  group  in  the  side  chain  as  well 

XNH2 
as  in  the  nucleus. 

301 


302  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

There  is,  therefore,  rather  a  bewildering  variety  of  aromatic 
amines;  but  we  need  consider  here  only  the  general  characteristics 
of  the  several  types  and  give  special  attention  to  a  few  individuals 
which  illustrate  these  types  and  are  of  practical  importance. 

In  the  first  place,  we  may  observe  that  in  contrast  with  the 
aliphatic  amines,  the  aromatic  amines,  in  which  the  amino  group 
is  united  with  nucleus  carbon,  are  neutral  in  reaction  instead  of 
strongly  alkaline,  and  do  not  absorb  carbon  dioxide.  The  amines 
containing  one  or  two  phenyl  groups  form  additive  salts  with  acids, 
but  these  salts  are  less  stable  than  the  salts  of  the  aliphatic  amines, 
being  more  or  less  hydrolyzed  in  solution  so  that  the  reaction  of 
then-  solutions  is  acid;  and  tertiary  amines  like  triphenylamine 
have  no  basic  properties  at  all.  The  aliphatic  amines,  on  the 
contrary,  form  stable  salts,  and  their  alkalinity  and  basicity  is 
greater  with  the  increase  in  the  number  of  alkyl  groups. 

These  differences  between  the  aromatic  nucleus  amines  and  the 
alkyl  amines  show  that  the  phenyl  radical  has  a  negative  character 
as  compared  with  the  rather  strongly  positive  alkyl  radicals.  This 
is  again  very  markedly  in  evidence  in  the  aromatic  hydroxyl  com- 
pounds— the  phenols  (p.  327) — which  have  distinctly  acid  proper- 
ties as  compared  with  the  alkyl  hydroxides — the  alcohols;  and 
is  also  more  or  less  marked  in  all  the  aromatic  derivatives. 

Aromatic  amines  which  have  the  amino  group  in  side  chains  are 
very  similar  to  the  alkyl  amines  in  their  properties,  and  may  be 
regarded  as  alkyl  amines  in  which  aryl  groups  have  been  sub- 
stituted for  hydrogen  in  the  alkyl  radical. 

The  presence  of  the  positive  amino  group  in  the  nucleus  increases 
the  reactivity  of  the  hydrogen  atoms  of  the  ring,  which  are  now 
readily  replaced  by  chlorine  or  bromine  and  yield  easily  to  sul- 
phonation  and  nitration. 

Primary  Amines 

Preparation. — i.  Aromatic  amines  with  the  amino  group  united 
with  nucleus  carbon — aryl  amines — -cannot  usually  be  made,  like 


AROMATIC   AMINES  303 

the  alkyl  amines,  by  the  action  of  ammonia  on  the  halogen  deriva- 
tives of  the  aromatic  hydrocarbons — the  halogen  in  this  position 
having,  as  we  have  seen,  little  reactivity.  The  reaction  becomes 
possible,  however,  when  the  nitro  group  is  also  present  in  the  ortho 
or  para  position  relative  to  the  halogen;  and  ortho-dinitrobenzene, 
and  ortho  and  para  nitrophenols  also  give  nitro-amido  com- 
pounds when  heated  with  ammonia.  Meta  compounds  do  not 
react.  Some  phenols  also  are  converted  into  amines  by  heating 
to  3oo°-35o°  with  ammonia-zinc  chloride. 

But  the  method  generally  employed  for  the  preparation  of  these 
amines  is  by  the  reduction  of  the  corresponding  nitro  compounds. 
The  reduction  is  usually  effected  by  means  of  tin  or  iron  and  hydro- 
chloric acid,  though  quite  a  variety  of  other  reducing  agents  are 
sometimes  employed.  Among  these  ammonium  sulphide  in 
alcoholic  solution  is  especially  useful  for  the  reduction  of  a  single 
nitro  group  in  a  compound  containing  two  or  three  such  groups. 

2.  Aromatic  aryl-alkyl  amines  with  the  amino  group  in  the  side 
chain  are  prepared  by  the  methods  used  for  alkyl  amines  (cf.p.  128). 

Aniline,  CeH5.NH2,  received  its  name  from  the  Spanish  term 
for  indigo,  anil,  as  it  was  first  obtained  by  the  destructive  dis- 
tillation of  this  substance  in  1826.  In  1834  it  was  discovered  in 
coal  tar,  and  shortly  before  had  been  made  by  the  reduction  of 
nitrobenzene.  It  was  not  till  1843,  however,  that  the  identity  of 
these  products  with  that  from  indigo  was  established.  Its  con- 
stitution is  determined  by  its  formation  from  compounds  of  known 
structure  and  by  the  products  of  its  reactions. 

The  amount  of  aniline  in  coal  tar  is  too  small  to  make  this 
source  of  any  importance.  The  very  large  amounts  that  are  used, 
chiefly  in  the  dye-stuff  industry,  are  obtained  from  coal  tar  ben- 
zene through  nitrobenzene.  The  reduction  of  the  nitrobenzene 
is  effected  by  means  of  iron-filings  and  hydrochloric  acid : 

C6H5.N02  +  3Fe  +  7HC1  = 

Nitrobenzene  CeHs-NH^HCl  +  3Fefcl2  +  2H2O 

Aniline  hydrochloride 


304  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

This  reaction  is  accomplished,  however,  with  the  use  of  a  very 
much  smaller  amount  (about  A)  of  hydrochloric  acid  than  is  indi- 
cated in  the  above  equation.  The  probable  explanation  of  this 
fact  is  that  iron  filings  and  water  effect  the  reduction,  the  small 
amount  of  ferrous  chloride  formed  at  first  acting  as  a  catalyzer. 

C6H5.NO2  +  2Fe  +  4H2O  =  C6H5.NH2  +  2Fe(OH)3 

When  the  reduction  is  ended,  lime  is  added  and  the  aniline  is 
distilled  with  steam.  Since  the  aniline  is  only  slightly  soluble  in 
water  and  is  a  little  heavier,  the  greater  part  of  it  separates  as  an 
oil  and  is  purified  by  redistillation,  while  the  "aniline-water"  is 
used  in  the  boiler  which  furnishes  steam  for  the  first  distillation. 

In  the  laboratory,  tin  and  strong  hydrochloric  acid  are  usually 
employed  for  the  reduction.  In  this  case  double  salts  of  tin  and 
aniline  are  formed,  which  are  decomposed  by  adding  caustic  soda 
before  distilling  with  steam.  Common  salt  added  to  the  distillate 
reduces  the  solubility  of  the  aniline,  which  is  then  extracted  with 
ether  and  distilled. 

Properties. — Aniline  is  an  oily  liquid  of  a  slight  and  characteris- 
tic odor,  and  is  poisonous.  When  freshly  distilled  it  is  colorless, 
but  turns  yellowish-brown  on  exposure  to  light  and  air.  This 
change  in  color  is  apparently  due  to  the  presence  of  traces  of 
sulphur  compounds,  which  can  be  removed  by  heating  with  ace- 
tone. Aniline  thus  treated  remains  colorless.  Its  specific  gravity 
is  1.024  (16°).  It  boils  at  183.7°.  I*1  water  it  dissolves  in  the 
proportion  of  about  one  part  to  30  of  water;  and  it  dissolves  water 
in  a  slightly  larger  proportion.  Aniline  is  dried  by  means  of 
solid  potassium  hydroxide  or  carbonate  (calcium  chloride  com- 
bines with  ammonia  and  amines,  and  is  consequently  not  suitable 
for  drying  these  compounds).  Aniline  is  miscible  in  every  pro- 
portion with  alcohol,  ether,  benzene,  etc.  It  is  readily  volatile 
(vith  steam. 

Reactions. — i.  Aniline,  like  most  amines,  unites  additively  with 
acids,  forming  crystalline  salts  which  are  mostly  soluble  in  water. 


AROMATIC   AMINES  305 

The  normal  sulphate,  (C6H5.NH2)2.H2S04,  and  the  oxalate, 
(C6H5.NH2)2.H2O4C2,  however,  are  only  slightly  soluble  in  cold 
water.  The  solutions  have  an  acid  reaction  from  hydrolysis ;  and 
the  salts  with  fatty  acids  are  converted  by  heating  into  the  more 
stable  substituted  acyl  amides  (anilides) : 

C6H5NH2.HO.OC.CH3  =  C6H5NH.OC.CH3  +  H2O-MIC1 

Aniline  also  forms  double  salts  such  as  (C6H5.NH2)2ZnCl2, 
(C6H5.NH2.HCl)2PtCl4,  and  (CeHe.NHa.HCl^SnCU. 

2.  Like  ammonia  and  the  alkyl  amines,  aniline  enters  into  re- 
action with  alkyl  halides  with  the  formation  of  mono-  and  dialkyl 
anilines,  such  as   C6H5.NH.CH3   and  C6H5N(CH3)2;   and  with 
alkyl  iodides  the  reaction  proceeds  to  the  formation  of  the  salt 
of  the  quaternary  ammonium  base,  e.g.,  trimethylphenylammonium 
iodide,  C6H5(CH3)3NI,  which  is  not  decomposed  by  cold  solutions 
of  alkalies,  and  from  which  silver  hydroxide  sets  free  the  strongly 
alkaline  base,  C6H5(CH3)3NOH. 

3.  Aniline  reacts  with  acid  chlorides  with  the  formation  of 
anilides  corresponding  to  the  amides: 

C6H5.NH2  +  CH3.CO.C1  =  C6H5.NHOC.CH3  +  HC1 

Aniline  Acetanilide 

4.  When  warmed  with  nitrous  acid,  solutions  of  salts  of  aniline 
and  other  primary  aryl  amines  evolve  nitrogen  with  the  exchange 
of  the  amino  group  for  the  hydroxyl  group,  as  in  the  case  of  the 
alkyl  amines;  but  at  room  temperature  or  in  ice  water  no  nitrogen 
is  set  free,  but  a  diazo  compound  is  formed  which  contains  two 
atoms  of  nitrogen: 

C6H6.NH2.HC1  +  HNO2  =  CeHg.NaCl  +  2H2O 

Benzenediazonium 
chloride 

The  diazo  compounds  are  quite  unstable,  as  is  indicated  by  the 
statements  just  made  in  regard  to  their  preparation,  and  they 
enter  into  many  important  reactions  (p.  315). 


306  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

5.  The  nucleus  hydrogen  of  aniline  is  more  readily  replaced 
than  that  of  benzene  by  halogens,  and  by  the  sulphonic  acid  and 
nitro  groups.     In  an  aqueous  solution  of  an  aniline  salt,  chlorine 
or  bromine  readily  give  trichlor  or  tribromaniline,  (i,  2,  4,  6). 

6.  Aniline  like  all  primary  amines  gives  the  carbylamine  test 
(cf.  p.  132). 

7.  Special  tests  for  aniline  are:  Dilute  solutions  of  aniline  or  its 
salts  give  (a)  a  violet  color  with  a  solution  of  bleaching  powder; 
(b)  a  precipitate  of  tribromaniline  with  bromine  water;  (c)  a  green, 
blue,  or  black  precipitate  when  treated  with  sulphuric  acid  and  a 
little  potassium  dichromate. 

Some  Derivatives  of  Aniline 

Acetanilide,  C6H5NH.OC.CH3,  is  the  most  important  of  a 
group  of  compounds  which  may  be  regarded  as  amides  in  which 
hydrogen  of  the  amido  group  is  replaced  by  aromatic  radicals — • 
in  this  case  by  phenyl.  Acetanilide  (or  phenyl-acetamide)  is 
usually  prepared  by  boiling  a  mixture  of  glacial  acetic  acid  and 
aniline  for  some  hours.  The  aniline  acetate  first  formed  loses  the 
elements  of  water  under  this  treatment,  leaving  the  acetanilide: 

C6H6.NH2.HO.OC.CH3  =C6H5.NH.OC.CH3  +  H2O 

It  may  also  be  made  by  the  other  methods  used  for  the  forma- 
tion of  amides  (p.  137):  treatment  of  aniline  with  acetyl  chloride, 
acetic  anhydride,  or  acetic  esters. 

Acetanilide  melts  at  116°  and  boils  at  304°.  It  is  much  more 
soluble  in  hot  water  than  in  cold,  and  crystallizes  well  from  its 
solution  in  glistening  plates.  It  is  not  hydrolyzed  by  water 
alone,  but  when  boiled  with  alkalies  or  acids  is  converted  into 
its  components,  aniline  and  acetic  acid  (or  acetate) : 

CeH5.NH.OC.CH3  +  KOH  =  C6H5.NH2  +  CH3CO.OK 

The  hydrogen  of  the  amido  group  can  be  replaced  by  a  second 
acetyl  group  by  the  action  of  acetyl  chloride  at  170°-!  80°,  giving 


AROMATIC   AMINES  307 

diacetanilide,  C6H5.N(OC.CH3)2.  This  melts  at  37°,  is  decom- 
posed  on  boiling,  and  is  readily  hydrolyzed  to  acetanilide  and 
acetic  acid  by  very  dilute  alkalies  or  acids. 

Acetanilide  and  the  corresponding  derivatives  of  other  aromatic 
amines  are  often  employed  in  the  preparation  of  aryl  amine  sub- 
stitution products,  since  the  presence  of  the  negative  acetyl  group 
renders  the  nucleus  hydrogen  less  reactive  and  so  makes  it  possible 
to  control  the  reaction  to  some  extent.  Thus,  while  with  aniline, 
bromine  water  produces  principally  tribromaniline,  acetanilide 
yields  monobromacetanilide  (para)  from  which  monobromaniline 
can  be  obtained  by  hydrolysis. 

Acetanilide,  formerly  known  as  "antifebrine,"  is  used  in  medi- 
cine, especially  in  headache  tablets. 

"Antipyrine"  is  a  derivative  of  aniline  whose  formula  is 

/N(CH3).C.CH3 
C6H5N/  || 

XCO    -    CH 

Sulphanilic  Acid,  NH2.C6H4.SO3H(i,  4),  or  para  aminoben- 
zenesulphonic  acid,  is  prepared  by  heating  aniline  and  concen- 
trated sulphuric  acid  to  i8o°-i9o°  for  four  or  five  hours.  Sulph- 
anilic acid  separates  from  its  solution  in  hot  water  in  crystals 
which  contain  two  molecules  of  water  and  are  efflorescent  It 
has  no  definite  melting  point,  and  chars  when  heated  to  about 
300°.  Sulphanilic  acid,  unlike  the  sulphonic  acids  of  the  hydro- 
carbons, is  only  slightly  soluble  in  cold  water.  It  dissolves 
readily,  however,  in  alkaline  solutions  from  the  formation  of 
alkali  salts.  It  forms  no  salts  with  acids,  the  basic  character 
of  the  amino  group  being  neutralized  by  the  negative  sulphonic 
group. 

It  is  oxidized  by  chromic  acid  into  quinone,  CeH4O2  (i,  4)  (p. 
3  50) .  When  fused  with  caustic  potash,  instead  of  yielding  amino- 
phenol,  HO.C6H4NH2,  it  gives  aniline.  The  diazo  compound 
formed  from  it  by  the  action  of  nitrous  acid  is  used  in  the  prepara- 
tion of  certain  dyes. 


308  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

The  ortho  and  meta  isomers  of  sulphanilic  acid  can  be  made  by 
the  reduction  of  the  corresponding  nitrosulphonic  acids. 

Nitranilines,  NCfe.CeH^NEk.  It  is  difficult  to  control  the  reac- 
tion of  concentrated  nitric  acid  on  aniline  so  as  to  obtain  a  mono- 
nitraniline,  but  nitration  of  acetanilide  gives  a  mixture  of  para 
and  ortho  nitroacetanilide  from  which  the  para  and  ortho  nitranil- 
ines  are  obtained  by  hydrolysis.  The  nitro  group  may  be  directed 
to  the  ortho  position  by  first  sulphonating  acetanilide.  This  gives 
the  para  sulphonic  acid,  and  when  this  is  nitrated  the  nitro  group 
enters  the  position  which  is  ortho  to  the  acetylamino  group  ;  and 
then  by  splitting  off  the  sulphonic  and  acetyl  groups,  ortho- 
nitraniline  is  obtained: 

NH.OC.CHa      NH.OC.CH3    NH.OC.CH3    NH2 

jN02  _ 

SO3H  SO3H 

Meta  nitraniline  is  readily  prepared  by  partial  reduction  of 
meta  dinitrobenzene  (p.  294)  by  means  of  ammonium  sulphide, 
or  stannous  chloride  and  hydrochloric  acid  in  alcoholic  solution: 


NO2.C6H4.NO2 

m-Dinitrobenzene  m-Nitraniline 

The  nitranilines  are  yellow  solids  which  crystallize  well  and 
are  very  slightly  soluble  in  water,  but  dissolve  readily  in  alcohol. 
They  are  weak  bases,  the  presence  of  the  nitro  group  not  quite 
neutralizing  the  basicity  of  the  amino  group.  The  basic  character 
varies  with  the  relative  positions  of  the  nitro  and  amino  groups: 
being  least  in  the  ortho  compound  and  greatest  in  the  meta 
nitraniline.  Their  melting  points  are  71.5°,  114°,  and  147°  for 
the  ortho,  meta,  and  para,  respectively. 

Para  nitraniline,  and  to  a  less  extent,  meta  nitraniline,  are 
employed  in  the  manufacture  of  azo-dyes. 

Tetranitro-aniline  is  one  of  the  most  powerful  explosives 
known,  and  another  similar  compound,  tetranitro-methylaniline, 


AROMATIC  AMINES  309 

called  "tetryl,"  is  used  for  detonators  in  place  of  mercuric  ful- 
minate. 

Alkyl  Derivatives  of  Aniline.  —  By  the  replacement  of  one  or 
both  hydrogen  atoms  of  the  amino  group  in  aniline  by  alkyl  groups, 
mixed  secondary  and  tertiary  amines  are  produced.  These  may 
be  prepared  by  the  direct  action  of  alkyl  halides  on  aniline; 
but  in  the  technical  manufacture  they  are  made  by  heating  aniline 
with  hydrochloric  or  sulphuric  acid  and  the  appropriate  alcohol  to 
about  200°: 


C6H5.NH2.HC1  +  CH3OH  =  CeHs.NH.CHa.HCl  +  H2O 
C6H5.NH.CH3.HC1  +  CH3OH  =  C6H6.N(CH3)2.HC1  +  H2O 

These  alkyl  derivatives  are  oily  liquids  which  smell  like  aniline. 
They  are  neutral  in  reaction,  but  are  stronger  bases  than  aniline, 
as  one  would  expect  from  the  presence  of  the  positive  alkyl  groups, 
and  are  very  similar  to  the  secondary  and  tertiary  alkyl  amines. 
Many  of  these  tertiary  amines  differ,  however,  from  the  tertiary 
aliphatic  amines,  in  reacting  very  readily  with  nitrous  acid  forming 
paranitroso  derivatives  which  are  of  importance  as  intermediate 
compounds  in  the  preparation  of  certain  dyes: 

N(CH3)2 
C6H5.N(CH3)2  +  HONO  =  C6H4%O      +H2O 


N 

Dimethyl-aniline  p-Nitroso-dimethyl-aniline 

Another  peculiar  reaction  of  these  amines  is  that  which  occurs 
when  their  hydrochloric  acid  salts  are  heated  to  about  300°. 
Under  these  conditions  the  alkyl  groups  are  transferred  from  the 
amino  group  to  the  nucleus,  with  the  formation  of  homologues  of 
aniline,  aniline  and  alkyl  chloride  being  perhaps  intermediate 
products: 
C6H5.NH(C2H5).HC1  -»C6H5.NH2  +  C2H5C1 

Ethyl-aniline  hydrochloride  _>  C2H5.C6H4.NH2.HC1 

Aminoethylbenzene  chloride 

This  is  an  important  technical  method  for  preparing  the  homo- 
logues of  aniline. 


310  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

The  quaternary  ammonium  salts  undergo  a  like  transformation: 
C6H5.N(CH3)3I  ->  CH3.C6H4.N(CH3)2.HI  -> 

Trimethyl-phenylam- 
monium  iodide 

(CH3)2.C6H3NH.(CH3)HI  -»  (CH3)3.C6H2.NH2.HI 

Tri-methyl-animoben- 
zene  iodide 
1:2:4:6 

By  this  reaction  it  has  proved  possible  to  prepare  a  homologue 
of  aniline  in  which  all  five  of  the  nucleus  hydrogen  atoms  are 
replaced  by  methyl,  (CH3)5C6NH2. 

The  most  important  of  these  alkyl  derivatives  is  dimethylani- 
line,  CeH5.N(CH3)2,  which  is  employed  in  the  manufacture  of  a 
number  of  dyes.  Monomethyl,  monoethyl,  and  diethyl  anilines 
are  also  prepared  in  the  industry,  but  their  use  is  far  less  than  that 
of  the  dimethylaniline. 

Novocaine,  a  local  anaesthetic,  is  the  hydrochloride  of  diethyl- 
ammo-ethyl-p-aminobenzoate : 

NH2.C6H4.CO.OC2H4.N(C2H5)2HC1 

Homologues  of  Aniline. — These  are  usually  prepared  from  the 
corresponding  nitro  compounds  when  the  hydrocarbon  is  obtain- 
able for  nitration.  In  many  instances  they  are  conveniently  made 
from  the  phenols,  whose  hydroxyl  group  is  replaced  by  the  amino 
group  by  heating  with  ammonia  in  the  presence  of  zinc  chloride, 
etc: 

ZnCh 

(CH8)  (C3H7)C6H3OH  +  NH3  =  (CH3)(C3H7)C6H3.NH2  +  H2O 

Thymol  Thymylamine 

A  third  method  is  by  heating  the  halogen  salts  of  the  alkyl- 
anilines  (p.  309). 

The  homologues  of  aniline  have  the  same  general  characteristics 
as  that  substance  and  require  no  further  description  here.  Impor- 
tant from  a  practical  standpoint  on  account  of  their  employment 
in  the  color  industry  are:  the  three  toluidines,  CH3.CeH4NH2, 
ortho  and  para  toluidines  being  used  almost  as  much  as  aniline 
itself.  The  xylidines,  (CH3)2.C6H3.NH2,  and  pseudocumidine, 
(CH3)3.CeH2.NH2  (1,2,4,5),  are  also  employed. 


AROMATIC   AMINES  311 

Secondary  and  Tertiary  Aromatic  Amines.  —  Diphenylamine, 
(C6H5)2NH,  is  made  on  a  large  scale  for  the  color  industry  by 
heating  aniline  with  aniline  hydrochloride  to  about  200°; 

C6H5.NH2  +  C6H5NH2.HC1  =  (C«H5)>NH  +  NH4C1 
It  can  also  be  made  by  heating  phenol  with  aniline  in  the  presence 
of  zinc  chloride: 

ZnCl2 
CeHg.NH,  +  CeKU.OH  =  (CeHs^NH  +  H2O 

The  tertiary  triphenylamine  (CeH^sN,  cannot  be  made  by  these 
methods.  It  is  formed,  but  in  small  amount,  when  the  sodium 
compound  of  diphenylamine  is  heated  with  brombenzene: 


N.Na  +  CeHsBr  =  (C6H5)3N  +  NaBr 

The  basic  character  of  aniline  is  much  weakened  by  the  intro- 
duction of  the  negative  phenyl  group.  Diphenylamine  forms 
salts  with  strong  acids,  but  they  are  at  once  decomposed  by  water; 
while  in  triphenylamine  the  basic  properties  have  wholly  dis- 
appeared. A  solution  of  diphenylamine  in  concentrated  sulphuric 
acid  serves  as  a  delicate  test  for  nitric  acid,  giving  a  blue  color 
with  traces  of  this  acid. 

Benzylamines 

Aromatic  amines  which  have  the  amino  group  in  a  side  chain 
have  received  the  name  of  benzylamines  from  the  simplest  mem- 
ber of  this  type,  C6H5.CH2.NH2  (CeHs.CH,  =  benzyl).  They  can 
be  made  by  the  methods  for  forming  the  aliphatic  amines,  and 
show  the  general  behavior  of  these  amines,  modified,  of  course,  by 
the  presence  of  the  phenyl  group.  Benzylamine,  and  the  other 
primary  amines  of  this  class,  are  isomeric  with  the  homologues  of 
aniline.  They  are  of  comparatively  little  importance. 

Benzylamine,  CeH5.CH2NH2,  isomeric  with  toluidine,  is  an 
alkaline  liquid  which  absorbs  carbon  dioxide  from  the  air.  It 
boils  at  185°,  and  is  miscible  with  water  in  every  proportion. 


3I2 


INTRODUCTION  TO   ORGANIC  CHEMISTRY 


Dibenzylamine,  (C6H5.CH2)2NH,  is  a  liquid  which  boils  above 
300°  but  decomposes  when  slowly  distilled.  It  is  insoluble  in 
water  and  does  not  absorb  carbon  dioxide. 

Tribenzylamine,  (CeHs.CH^sN,  crystallizes  from  hot  alcohol, 
melts  at  91°,  and  combines  with  methyl  iodide  to  tribenzyl- 
methyl-ammonium  iodide. 

Derivatives  of  these  amines,  such  as  benzyl  aniline,  CeH6 .  CH2 .  - 
NH.CeHs,  and  dibenzylaniline,  (Cel^.CHa^N.CeHB,  can  also  be 
obtained. 

SOME  AMINO  DERIVATIVES  OF  BENZENE 


Aniline 

o-Toluidine 

m-Toluidine 

P-Toluidine 

p-E  thylphenylamine 

Benzylamine 

Methylaniline 

Dimethylaniline 

o-Phenylene  diamine 

m-Phenylene  diamine 

p-Phenylene  diamine 

Toluylene  diamine 

Diphenylamine 

Triphenylamine 

Acetanilid 

Diacetanilide 


C6H6.NH2 

CH3.C6H4.NH2  (i,  2) 
CH3.C6H4.NH2  (i,  3) 
CH3.C6H4.NH2  (i,  4) 
C2H6.C6H4.NH2  (i,  4) 
C6H5.CH2.NH2 
C6H5.NH(CH3) 
C6H5.N(CH3)2 
C6H4(NH2)2  (i,  2) 
C6H4(NH2)2  (i,  3) 
C6H4(NH2)2  (i,  4) 
CH3.C6H3(NH2)2  (1,3,4) 
(C6H6)2NH 
(C6H6)3N 
C6H5.NH.CO.CH3 
C6H6.N(CO.CH3)2 


Melting 

Boiling 

point 

point 

-6.2° 

183-184° 

liquid 

199.7 

liquid 

203.3 

45 

200.4 

-5 

214 

185 

o 
IQ7  ,  r 

2-5 

•*  vo  *  o 

193 

1  02-  J  03 

257 

63 

283 

140 

267 

1         88.5 

265 

54 

302 

127 

116 

304 

37     145  (15  mm.) 


CHAPTER  XXIII 
DIAZO  COMPOUNDS 

Attention  has  already  been  called  to  the  existence  of  a  class  of 
compounds  which  are  formed  by  the  action  of  nitrous  acid  on  the 
salts  of  the  primary  aromatic  amines  (cf.  p.  305).  The  immediate 
products  of  this  reaction  are  unstable,  very  reactive  substances 
whose  composition  is  of  the  type,  CeHU.^Cl  or  CeHs.^NOa. 
They  were  called  diazo  compounds  from  the  fact  that  they  con- 
tain two  united  atoms  of  nitrogen  (French,  azote).  These  com- 
pounds were  discovered  in  1858  by  Peter  Griess,  and  the  many 
useful  reactions  which  they  give  quickly  established  their  im- 
portance in  synthetic  and  technical  chemistry. 

Preparation.  —  Although  diazo  compounds  can  be  made  in  other 
ways,  the  method  which  is  of  the  first  importance  is  by  means  of 
nitrous  acid  acting  on  the  salt  of  the  amine: 


C6H5.NH2.HC1  +  HONO  =  CeH^Cl  +  2H2O 

Aniline  hydrochloride  Phenyldiazonium 

chloride 

The  reaction  is  carried  out  by  adding  sodium  nitrite  or  amyl 
nitrite  to  an  acid  solution  of  the  amine;  or  less  often  by  leading 
into  a  solution  of  the  amine  salt  oxides  of  nitrogen  evolved  by  the 
action  of  nitric  acid  on  arsenic  trioxide  or  starch.  The  operation 
is  conducted  in  solutions  cooled  by  ice  on  account  of  the  instability 
of  the  diazo  compounds  at  higher  temperatures.  The  diazo 
compounds  made  in  this  way  are  usually  not  isolated,  but  im- 
mediately employed  in  solution  for  various  reactions.  The  solid 
compounds  can,  however,  be  prepared  by  taking  advantage  of 
their  small  solubility  in  alcohol  and  their  insolubility  in  ether. 

Properties.  —  Since  the  isolation  of  these  substances  is  seldom 

313 


314  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

necessary,  for  the  purposes  to  which  they  are  applied,  compara- 
tively little  is  known  of  their  individual  properties,  in  spite  of  the 
fact  that  almost  every  known  primary  aromatic  amine  has  been 
"diazotized."  They  are  colorless,  crystalline  solids  which  are 
easily  soluble  in  water.  In  the  dry  solid  state  they  are  very  explo- 
sive when  heated,  and  in  some  cases  when  struck.  Diazo- 
benzenenitrate,  in  particular,  is  more  violently  explosive  than 
nitrogen  iodide  or  mercury  fulminate. 

They  are  well  characterized  salts,  and  they  form  double  salts, 
such  as  (CeHe^^PtCle,  which  are  analogous  to  those  of  the 
alkalies.  The  chlorides  and  nitrates  are  not  hydrolyzed  in  solu- 
tion, as  is  shown  by  their  neutral  reaction,  and  they  are  ionized 
to  the  same  high  degree  as  potassium  chloride  and  nitrate.  The 
carbonates,  which  are  formed  in  solution  by  digesting  diazo- 
nium  halides  with  silver  carbonate,  are,  like  potassium  carbonate, 
soluble,  and  have  a  strong  alkaline  reaction.  On  treatment  of  a 
solution  of  the  chlorine  compound  with  silver  oxide,  silver  chloride 
is  precipitated  and  the  solution  becomes  strongly  alkaline  from 
the  formation  of  the  diazonium  hydroxide. 

Structure. — 'The  facts  that  have  just  been  stated  show  that  the 
solutions  of  these  compounds  contain  a  highly  positive  ion, 
CeH5N2,  resembling  in  character  the  potassium  or  ammonium 
ion,  and  in  which  one  nitrogen  atom  probably  has  the  valence  of 
five,  as  in  ammonium.  This  ion  or  radical  is,  by  analogy,  called 
diazonium  and  the  structure  of  the  diazonium  salts  is  represented 


by   the   formula,  Ar.N\      (in  which  Ar   stands   for   the   aryl 

XX 
radical).     The  strong  base  which  is  produced  by  the  action  of 

^N 

silver  oxide   (hydroxide)   on  a    diazonium    salt  is  Ar.Nv 

\OH 

analogous  to  ammonium  hydroxide.  This  structure  of  the  diazo- 
nium compounds  accords  with  the  simplest  explanation  of  the 
reaction  by  which  they  are  formed: 


DIAZO   COMPOUNDS  315 

Ar.N/  ' 3  +  H— O-- N  =  O    =    Ar.N/     +  2H2O 

\x  NX 

Amine  salt  Diazonium  salt 

The  nitrogen  atom  in  the  amine  salt  has  the  valence  of  five, 
that  in  nitrous  acid  is  a  triad,  and  the  formation  of  the  diazonium 
salt  is  the  result  of  simple  replacement  of  three  hydrogen  atoms 
by  triad  nitrogen. 

Reactions. — The  diazo  group  can  be  replaced  by: 

1.  Hydroxyl. — This  usually  takes  place  on  warming  the  aqueous 
solution  of  a  diazonium  salt,  or  allowing  it  to  stand  at  ordinary 
temperature: 

C6H5.N2C1  +  H2O  =  CeHs.OH  +  N2  +  HC1 

If  a  diazonium  nitrate  is  used,  the  resulting  phenol  is  liable  to  be 
nitrated  by  the  nitric  acid  liberated  in  the  reaction. 

2.  Alkoxyl. — In  many  cases  an  alkoxyl  group  may  be  substi- 
tuted by  boiling  the  dry  diazonium  salt  with  absolute  alcohol: 

(CH3)3C6H2.N2.SO4H  +  C2H5OH  = 

(CH3)3C6H2.OC2H5  +  N2+H2SO4 

The  reaction  with  alcohol  in  other  cases  results  in  the  substitution 
of: 

3.  Hydrogen. — In  this  reaction  the  alcohol  is  oxidized  to  alde- 
hyde: 

C6H5.N2C1  +  C2H6OH  =  C6H6  +  N2  +  CH3.CHO  +  HC1 

Which  of  these  two  reactions  with  alcohol  occurs,  depends  on  the 
nature  of  the  diazonium  compound  and  of  the  alcohol,  as  well  as 
on  the  conditions  of  the  reaction.  The  hydrogen  replacement  is 
favored  by  the  presence  of  negative  groups  in  the  aryl  ring,  espe- 
cially if  they  are  in  the  ortho  position.  Hydrogen  can  also  be 
substituted  for  the  diazo  group  by  treatment  of  the  diazonium 
salt  with  an  alkaline  stannous  solution;  or  indirectly,  by  formation 


316  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

of  diazonium  iodide  and  reduction  of  this  by  distillation  from  zinc 
dust;  or  through  the  hydrazine  (p.  318). 

4.  Halogens  can  be  introduced  in  place  of  the  diazo  group  in 
several  ways:  (a)  By  heating  with  the  halogen  acids,     (b)  By 
distilling  the  platinum  double  salt  with  sodium  carbonate,     (c) 
By  treating  the  solution  of  the  corresponding  diazonium  halide 
with  finely  divided  copper,  which  usually  decomposes  it  in  the 
cold  (Gattermann's  reaction),     (d)  Most  conveniently  by  heating 
the  diazonium  chloride  or  bromide  with  cuprous  chloride  or  bro- 
mide (Sandmeyer's  reaction),     (e)  Iodine  is  introduced  most 
simply  by  pouring  a  strongly  acid  solution  of  diazonium  sul- 
phate into  a  solution  of  potassium  iodide. 

5.  Cyanogen  is  substituted  by  means  of  Sandmeyer's  reaction, 
using  a  hot  solution  of  potassium  cuprous  cyanide.     Since  the 
resulting  cyanide  (nitrile)  is  readily  hydrolyzed  to  the  correspond- 
ing acid,  this  reaction  serves  as  a  useful  method  for  introducing 
the  carboxyl  group  into  aromatic  compounds. 

6.  Aromatic  hydrocarbon  groups,  such  as  toluyl,  can  be  intro- 
duced by  warming  the  dry  diazonium  salt  with  an  excess  of  the 
corresponding  hydrocarbon  —  the  reaction  being  aided,  if  neces- 
sary, by  the  presence  of  aluminium  chloride: 


C6H5N2C1  +  CeHs.CHs  =  CeHs.CeH^CHg  +  N2  +  HC1 

7.  Nitro  Group.  —  This  replacement  is  seldom  made,  but    is 
occasionally  useful,  as  in  making  /3-nitronaphthalene  which  can- 
not be  obtained  by  direct  nitration,  while  the   corresponding 
amine  is  easily  prepared.     The  nitro  group  is  introduced  tby 
treating  the  diazonium  solution  with  an  equivalent  amount  of 
sodium  nitrite  and  then  decomposing  the  diazonium  nitrite  with 
cuprous  oxide. 

Other  replacements  can  be  made,  but  these  which  have  been 
described  are  the  most  important  ones. 
Reactions  in  which  the  diazo  group  is  not  replaced  are: 

8.  The   formation   of  diazoamino   and   aminoazo   compounds. 


DIAZO   COMPOUNDS  317 

By  the  action  of  a  diazonium  salt  on  amines  (aromatic  or  aliphatic) 
the  first  product  is  a  diazoamino  compound: 


C6H5N2C1  +  C6H5.NH2  =  CeHs.Na.NH.CeHs  +  HC1 

Diazoaminobenzene 

These  compounds  are  very  weak  bases.  They  are  converted 
into  diazonium  chlorides  or  bromides  and  the  corresponding 
amine  salts  by  the  action  of  concentrated  hydrochloric  acid,  or 
by  hydrobromic  acid  in  ethereal  solution  : 

NO2.C6H4.N2.NH.C6H4.NO2  +HC1  = 

Diazoaminonitrobenzene 

N02.C6H4.N2C1  +  NO2.C6H4.NH2.HC1 

Nitrobenzene  diazonium  Nitraniline  hydrochloride 

chloride 

The  most  remarkable  property  of  the  diazoamino  compounds 
is  that  of  molecular  rearrangement  which  occurs  in  their  solu- 
tions in  the  free  amines  when  a  little  of  the  amine  salt  is  also 
present,  and  under  some  other  conditions.  If  the  para  position 
in  the  amine  group  is  unsubstituted,  a  para  aminoazo  compound 
is  formed: 

NH.N  =  N  N  =  N 


NH2 

Diazoaminobenzene  p-Aminoazobenzene 

The  aminoazo  compounds  are  of  great  importance  in  the  dye- 
stuff  industry. 

9.  Diazonium  salts  react  with  phenols  in  alkaline  solutions  to 
form  para  hydroxyazo  compounds: 


C6H5.N2C1  +  CeHsOH  =  CeH^.CeKU.OH  +  HC1 

Hydroxyazobenzene 

A  great  variety  of  dyes  are  made  by  similar  reactions. 

10.  By  partial  reduction  of  diazonium  salts  hydrazines  are 


318  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

produced,  which  may  be  regarded  as  hydrazine,  NH2.NH2,  in 
which  a  hydrogen  atom  is  replaced  by  an  aryl  group.  Phenyl- 
hydrazine  hydrochloride,  CeH5.NH.NH2.HCl,  for  instance,  can 
be  made  by  treating  benzenediazonium  chloride  with  the  proper 
amount  of  stannous  chloride  and  hydrochloric  acid: 

C6H5.N2C1  +  4H  =  C6H5.NH.NH2.HC1 

The  hydrazines  are  pronounced  mono-acid  bases.  They  are 
set  free  from  their  salts  by  sodium  hydroxide  in  the  form  of  oils 
or  solids  which  are  sparingly  soluble  in  water  and  nearly  insoluble 
in  strong  alkalies;  but  they  dissolve  readily  in  alcohol  and  ether. 
They  are  very  sensitive  to  oxidizing  influences,  and  hence  are 
strong  reducing  agents,  even  dilute  solutions  reducing  Fehling's 
solution  in  the  cold.  The  first  product  of  the  oxidation  of  primary 
hydrazines  is  the  corresponding  diazo  compound.  Treatment 
with  copper  sulphate  or  ferric  chloride  under  certain  conditions 
results  in  the  replacement  of  the  hydrazine  group  by  hydrogen, 
and  this  reaction  serves  as  a  means  for  converting  amines  into  the 
corresponding  hydrocarbons,  and  also  for  the  quantitative  deter- 
mination of  the  hydrazine  by  measurement  of  the  nitrogen  which 
is  evolved: 

C6H5.NH.NH2  +  2CuSO4  +  H2O  =  CeH6  +  Cu2O  +  N2  +  2H2SO4 

Phenylhydrazine  is  a  poisonous  oil.  It  is  made  commercially 
for  the  preparation  of  "antipyrine"  and  certain  dyes. 

The  hydrazines  react  with  compounds  containing  the  carbonyl 
group,  forming  with  aldehydes  and  ketones,  hydrazones,  whose 
service  in  the  characterization  of  carbonyl  compounds — espe- 
cially the  sugars — has  already  been  noticed  (p.  208). 

Further  Discussion  of  the  Structure  of  Diazo  Compounds. — 
We  have  seen  that  diazonium  hydroxide  is  a  strong  base  whose 
constitution  is  like  that  of  ammonium  hydroxide.  Its  solutions, 
nevertheless,  react  with  potassium  hydroxide  forming  a  potassium 
diazoate  by  replacement  of  the  hydroxyl  hydrogen  by  potassium. 


DIAZO   COMPOUNDS  319 

In  this  relation,  therefore,  it  behaves  as  an  acid.  Now  while 
we  know  several  metal  hydroxides  which  play  the  double  part 
of  base  and  acid,  such  as  the  hydroxides  of  zinc,  aluminium,  and 
tin — their  compounds  are  weak  bases  and  very  weak  acids,  and 
the  alkali  salts  they  form  are  usually  very  unstable.  But 
here  we  have  a  very  strong  base  which  also  forms  a  distinct  alkali 
salt.  The  explanation  is  found  in  a  probable  rearrangement 
of  the  diazo  group,  so  that  in  acting  as  a  weak  acid  toward  potas- 
sium hydroxide  its  structure  becomes  Ar.N:N  OH,  isomeric  with 


the    base,   Ar.N^  .      The  hydroxyl  group  has  shifted,  and 

X)H 

the  valence  of  the  pentad  nitrogen  atom  has  dropped  to  three, 
with  the  change  from  strong  base  to  weak  acid. 

Potassium  benzenediazoate,  CeH5N:NOK,  when  heated  with 
strong  potassium  hydroxide  is  changed  to  a  more  stable  iso-form 
which  is  considered  to  be  a  stereoisomer  of  the  first.  The  arrange- 
ments of  the  groups  in  these  two  salts  may  be  represented  by  pro- 
jection formulas  which  are  similar  to  those  for  maleic  and  fumaric 
acids  (p.  186),  the  "anti"  arrangement  being  the  stable  one, 

C6H5.N  C6H5.N 

II  II 

KO.N  N.OK 

Normal  or  syn-diazoate  Iso-  or  anti-diazoate 

The  only  hydroxide  which  can  be  isolated  is  the  anti-diazo 
it  hydroxide,  which  is  obtained  in  the  form  of  unstable  crystals  by 
nprecipitating  an  anti-diazoate  with  acetic  acid  at  a  low  tempera- 
ture. On  dissolving  in  water  it  changes  into  another  isomeric 
iform,  nitrosamine, 

C6H5.NH 


N=O 


This  theory  as  to  the  structure  of  the  diazo  compounds  explains 
pie  reactions  which  result  in  the  replacement  of  the  diazo  group  as 


32O  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

follows:  The  diazonium  salts  first  form  addition  products  with 
the  reagent  employed,  and  then  these  break  down  into  syn-diazo 
compounds,  which  in  turn  decompose  with  loss  of  nitrogen.  In 
the  replacement  by  hydroxyl,  for  instance,  the  steps  would  be: 

Ar                                  Ar     OH  Ar        OH 

|                     OH           |         |  -II  Ar.OH 

N  =  N  +    |        -+N=N  ->      N  =  N      -»       + 

|                    H              |         |  N  =  N 

Cl                                 Cl     H  +  C1H 

In  the  case  of  the  reaction  with  alcohol,  which  sometimes  sub- 
stitutes alkoxyl  and  sometimes  hydrogen,  two  different  addition 

Ar  Ar       O.C2H5     Ar     O.C2H5    ArO.C2H6 

I  O.C2H6       ||  |.|  + 

(i)N  =  N+|  ->N  =  N         ->N  =  N  ->N  =  N 

I  H  |        |  + 

Cl  Cl    H  HC1 

products  can  be  formed,  and  the  formation  of  one  or  the  other 
determines  the  final  product. 

Ar  Ar      H  Ar      H 

I  H  |          |  ||  ArH 

(2)N  s  N  +    |       -*  N  =  NH       -»  N  =  N  + 

O.C2H5  ||  +  N^N. 

Cl  Cl       O.C2H5   C1H  +  CH3CHO 

The  other  reactions  may  be  explained  in  a  similar  way. l 

1  For  a  good  exposition  of  Hantzsch's  theory  of  the  structure  of  diazo  com- 
pounds, see  Sidgwick's  "Organic  Chemistry  of  Nitrogen." 


CHAPTER  XXIV 
AZO  AND   OTHER  NITROGEN   COMPOUNDS  —  DYES 

In  discussing  the  reactions  of  the  nitro  compounds,  we  have 
noticed  that  while  the  amines  —  anilines  —  are  the  final  products  of 
the  reduction  of  these  substances,  the  reduction  can  be  controlled 
by  the  use  of  certain  mild  reducing  agents,  so  that  intermediate 
compounds  are  obtained.  These  are  illustrated  by  the  following, 
which  are  products  of  different  reductions  of  nitrobenzene: 

Phenylhydroxylamine,  C6H5.NH.OH 
Azoxybenzene,  C6H5.N  -  -  N.C6H5 


Azobenzene, 
Hydrazobenzene, 

All  of  these  substances  are  converted  into  the  corresponding 
amines  —  e.g.,  aniline  —  by  strong  reducing  agents,  and  they 
usually  do  not  appear  at  all  when  acid  reducing  agents  act  on 
the  nitro  compounds. 

Phenylhydroxylamine  is  formed  when  nitrobenzene  is  reduced 
by  a  neutral  reducing  agent,  such  as  aluminium  amalgam  or  zinc 
dust  and  hot  water. 

It  forms  white  crystals  which  melt  at  81°.  It  reduces  an 
ammoniacal  solution  of  silver  nitrate  and  Fehling's  solution  in  the 
cold,  and  in  aqueous  solution  is  quickly  oxidized  by  the  air  into 
azoxybenzene.  By  chromic  acid  it  is  oxidized  to  nitrosobenzene, 
CeHs.NO,  which  is  readily  reduced  to  aniline.  Phenylhydroxyl- 
amine acts  toward  acids  as  a  base,  but  when  warmed  with  inor- 
21  321 


322  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

ganic  acids  suffers  a  transformation  by  rearrangement,  into  the 
isomeric  p-aminophenol,  NEk.CeH^OH. 

Azoxy  compounds  are  formed  by  reduction  of  the  nitro  com- 
pounds with  weak  alkaline  reducing  agents,  such  as  an  alcoholic 
solution  of  sodium  hydroxide.  Azoxybenzene, 

CeHs.N  -  N.C6H6 
\0/ 

is  a  light  yellow  crystalline  substance,  which  melts  at  36°. 

Azo  compounds  can  be  prepared  from  the  nitro  compounds 
by  the  use  of  somewhat  stronger  alkaline  agents  —  sodium  amal- 
gam, alcoholic  solutions  of  an  alkali  with  zinc  dust,  or  stannous 
chloride  with  an  excess  of  sodium  hydroxide.  The  azo  compounds 
can  also  be  prepared  by  further  reduction  of  the  azoxy  compounds 
by  the  agents  just  mentioned,  or,  very  conveniently,  by  their 
distillation  from  iron  filings;  or  by  oxidation  of  the  primary 
aromatic  amines  (by  alkaline  permanganate  or  hydrogen  peroxide)  : 

C6H6NH2  +  H2N.C6H5  +  2O 


The  azo  compounds  are  strongly  colored  substances.  They 
are  insoluble  in  water,  acids,  and  alkalies,  but  dissolve  in  ben- 
zene, alcohol  and  ether.  They  are  very  stable,  and  in  this  re- 
spect form  a  striking  contrast  to  the  diazo  compounds,  which 
also  contain  two  united  nitrogen  atoms.  By  reducing  agents, 
however,  the  azo  compounds  are  readily  changed,  being  con- 
verted, according  to  the  conditions,  into  hydrazo  compounds  or 
into  the  amines.  Azobenzene  forms  orange  red  crystals,  melts  at 
68°  and  boils  at  295°.  While  the  azo  hydrocarbons  are  not  them- 
selves dyes,  a  large  number  of  the  most  important  dyes  are 
derivatives  of  these  compounds  and  are  known  as  the  azo  dyes 

(P-  325). 

Hydrazo  compounds,  such  as  hydrazobenzene,  CeH5.NH.NH.- 
CeHs,  are  formed  in  the  last  step  before  the  amine  in  the  reduc- 
tion of  nitro  compounds.  They  are  formed  by  the  reduction 


AZO   AND   OTHER  NITROGEN  COMPOUNDS  323 

of  nitro,  azoxy,  or  azo  compounds  by  an  alcoholic  solution  of 
ammonium  sulphide,  or  other  alkaline  reducing  agents,  and 
also  by  electrolytic  reduction  of  the  nitro  compounds  in  the 
presence  of  an  alkali. 

The  hydrazo  compounds  are  colorless  substances,  which  are 
neutral  in  character.  In  the  air  they  suffer  a  partial  oxidation, 
especially  when  moist,  into  the  strongly  colored  azo  compounds, 
and  this  change  occurs  readily  with  other  mild  oxidizing  agents. 
When  strongly  heated  they  are  converted  into  a  mixture  of  azo 
compounds  and  amines: 

2C6H5.NH.NH.C6H5  =  C6H5.N:N.C6H5+  2C6H5NH2. 

Strong  acids  cause  a  molecular  rearrangement,  hydrazobenzene 
being  transformed  into  benzidine  with  some  of  the  isomeric 
diphenyline, 


and 

X_X 

Hydrazobenzene  Benzidine 

NH2 


Diphenyline 

Benzidine,  p-diaminodiphenyl,  crystallizes  in  colorless  plates 
which  melt  at  122°.  It  is  a  diacid  base,  and  is  the  starting  point 
for  the  manufacture  of  a  large  group  of  dyes  of  the  Congo  series. 

Dyes 

The  azo  dyes  exceed  in  number  those  of  any  other  class,  and 
are  perhaps  the  most  important  of  the  manufactured  dyes.  The 
first  commercial  dye  made  from  coal  tar.  products  was  prepared 
by  W.  H.  Perkin  in  1857  by  the  oxidation  of  an  impure  aniline 
sulphate  with  chromic  acid.  The  manufacture  of  this  dye, 
"  mauve,"  and,  soon  after,  of  a  number  of  others  from  aniline  and  its 
homologues,  led  to  their  designation  as  "aniline  dyes,"  a  term 


324  INTRODUCTION   TO   ORGANIC  CHEMISTRY 

which  is  now  often  used  for  all  of  the  dyes  which  are  made 
from  the  aromatic  substances  distilled  from  coal  tar.  Many 
of  these  dyes,  however,  are  in  no  way  derived  from,  or 
related  to,  aniline,  so  that  the  general  name  of  "coal  tar  dyes" 
is  a  more  appropriate  one. 

A  dye  must  be  soluble  in  water,  or  readily  brought  into  a  soluble 
form,  and  have  the  property  of  adhering  to  the  fiber  either  directly, 
or  after  the  fiber  has  been  treated  with  certain  agents  called 
"mordants."  Dyes  which  color  the  fiber  permanently  without 
a  mordant  are  called  "direct"  or  "substantive"  dyes,  while 
those  which  require  a  mordant  are  "mordant"  or  "adjective" 
dyes.  Many  dyes  are  either  substantive  or  adjective  according 
to  the  character  of  the  fiber.  Substantive  dyes  for  wool  or 
silk  are  more  common  than  for  cotton  and  linen.  Many  different 
substances  serve  as  mordants;  those  most  used  being,  for  basic 
dyes,  tannic  acid  and  compounds  of  it  with  antimony;  and  for 
acid  dyes,  acetates  of  aluminium,  chromium,  or  iron,  from  which 
the  hydroxides  of  the  metals  are  separated  on  the  cloth  by  pass- 
ing through  a  weak  basic  bath  or  steaming.  The  cloth  prepared 
by  treatment  with  the  mordant  is  dyed  by  the  formation  of  in- 
soluble compounds  of  the  dye  with  the  hydroxides.  The  mordant 
frequently  modifies  the  color  produced  by  the  dye.  In  some 
cases,  a  fabric  is  dyed  by  developing  the  dye  on  the  fibers  by 
the  use  of  appropriate  reagents  in  the  dye-bath.  The  results 
are  called  "ingrain"  colors  and  are  remarkably  "fast,"  i.e., 
resistant  to  washing  and  acids. 

There  are  certain  groups  which  are  almost  always  present  in 
colored  organic  compounds.  The  most  important  of  these 
"chromophore"  groups  are:  The  nitro  group,  —  NO2,  the 
azo  group,  —  N  =  N  — ,  and  the  quinoid  group  (p.  352): 

/c  -  cx 

=  c  c  = 

\c-c/ 


AZO   AND   OTHER   NITROGEN   COMPOUNDS  325 

The  colors  of  the  compounds  containing  these  groups  are  often 
much  modified  by  the  further  introduction  of  atoms  or  groups 
which  of  themselves  produce  no  color;  such  as  phenyl,  alkyl 
groups  or  bromine.  With  the  increase  in  molecular  weight 
which  is  brought  about  in  this  way  there  is  in  general  a  deepen- 
ing of  the  shade,  or  a  change  in  color,  usually  in  the  order  yellow, 
orange,  red,  violet,  blue,  black. 

But  the  presence  of  a  chromophore  group  does  not  of  itself 
make  the  compound  a  dye.  There  must  be  also  a  basic  or  acid 
group  which  will  enable  it  to  combine  with  the  fiber  or  mordant. 
Such  groups  are  called  "auxochrome"  groups,  and  the  most  im- 
portant of  them  are  the  amino  and  hydroxyl  (phenol)  groups. 
Thus  nitrobenzene,  which  is  pale  yellow,  is  not  a  dye,  but 
p-nitraniline,  NO2.C6H4.NH2,  and  p-nitrophenol,  NO-j.CgHs.OH, 
are  dyes;  and  azobenzene,  though  deeply  colored,  is  incapable  of 
dyeing  cloth,  while  aminoazobenzene  and  derivatives  of  it  form 
a  large  number  of  well-known  dyes. 

The  acid  groups  -  CO.OH  and  -  S03H  do  not  have  the 
power  of  changing  a  colored  compound  into  a  dye,  but  the 
sulphonic  group  is  often  introduced  to  give  an  insoluble  dye  the 
solubility  necessary  for  use  in  dyeing. 

Azo  dyes  are  aminoazo  or  oxyazo  compounds  and  are  made 
by  treating  diazonium  salts  with  aromatic  amines  or  phenols: 

C6H5.N/      +  C6H4(NH2)2  =  <f  \N:N/   \NH2.HC1 

\Q  \ /  \ / 

Phenylene  diamine  NH2 

"Chrysoidine" 
Diaminoazobenzene 

C6H5.N/      +  C6H5.OH  =  /~\N:N/~\OH  +  HC1 

\Q  \ / 

Oxyazobenzene 

In  the  reaction  between  the  diazonium  salt  and  the  amine. 
diazoamino  compounds  are  sometimes  the  immediate  products, 


326  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

but  are  readily  converted  into  the  aminoazo  compounds  in  the 
presence  of  the  amine  and  its  hydrochloride  (cf.  p.  317). 

As  indicated  in  the  equation  just  given,  a  para-hydrogen  atom 
in  the  amine  or  phenol  is  the  one  which  is  first  replaced. 

Since  practically  all  aromatic  primary  amines  can  be  diazotized 
and  the  resulting  diazonium  salts  react  with  all  aromatic  amines, 
primary,  secondary,  and  tertiary,  and  with  all  phenols  (hydroxyl 
derivatives),  the  number  of  azo  dyes  that  are  theoretically  pos- 
sible is  enormous.  The  first  of  these  dyes  which  was  made  com- 
mercially was  chrysoidine  (1876),  an  orange  dye,  whose  formation 
is  given  in  the  first  of  the  equations  above. 

These  dyes,  and  colored  organic  substances  generally,  are  con- 
verted by  reducing  agents  into  colorless  substances,  the  so- 
called  leuco  compounds,  which  usually  return  readily  to  their 
original  color  even  on  exposure  to  the  air.  The  leuco  compounds 
of  the  azo  dyes  are  the  corresponding  hydrazo  compounds. 

The  simplest  of  the  azo  dyes  are  yellow.  With  increase  of 
molecular  weight  through  the  presence  of  substituents  they 
become  darker,  changing  through  the  range  of  colors  already 
given  (p.  325).  They  are  crystalline  substances,  and  most  of 
them  are  insoluble,  so  that  they  are  frequently  employed  in  the 
form  of  their  sulphonic  acids  which  are  made  by  treatment  with 
concentrated  sulphuric  acid. 

Methyl  orange  (helian thine)  is  the  sodium  salt  of  dimethyl- 
amino-azobenzene  sulphonic  acid,  HSOs.CeH^^.CeEU.NCCHs^. 
It  is  prepared  by  "condensing"  dimethyl  aniline  with  the  diazo 
compound  of  sulphanilic  acid  (p.  307).  It  dyes  silk  and  wool  a 
bright  orange,  and  is  much  used  as  an  indicator  in  volumetric 
analysis,  the  orange  being  changed  sharply  to  red  by  acids. 

Congo  red  is  described  on  page  387. 


CHAPTER  XXV 
PHENOLS— AROMATIC  ALCOHOLS— ETHERS 

As  in  the  case  of  other  derivatives  of  the  aromatic  group,  the 
hydroxyl  compounds  fall  into  two  classes.  The  phenols  are 
compounds  in  which  the  hydroxyl  group  or  groups  are  united  to 
nucleus  carbon,  while  substances  containing  this  group  in  a  side 
chain  are  aromatic  alcohols.  The  aromatic  alcohols  are  very 
much  like  the  alcohols  of  the  aliphatic  series  in  their  general 
behavior,  but  the  phenols  are  quite  different  from  alcohols  in 
most  of  their  properties.  The  differences  between  these  two 
classes  of  hydroxyl  compounds  are,  in  general,  of  the  kind 
already  noticed  in  other  derivatives  of  the  aromatic  hydrocarbons 
in  which  aryl  and  alkyl  groups  both  are  present. 

The  aromatic  ethers  are  compounds  in  which  two  aryl  radicals 
or  an  aryl  and  alkyl  radical  are  linked  together  by  oxygen. 

Phenols 

A  number  of  phenols  are  among  the  products  of  the  destructive 
distillation  of  various  natural  organic  substances.  Thus  phenol, 
hydroxybenzene,  C6H5OH,  the  simplest  of  the  phenols,  and  the 
cresols,  C7H7OH,  formed  thus  from  coal,  are  obtained  from 
coal  tar;  and  pyrogallol,  a  trihydric  phenol,  C6H3.(OH)3,  is  ob- 
tained by  heating  gallic  acid,  which  occurs  naturally  in  oak- 
galls  and  is  also  prepared  from  tannin.  The  characteristics  of 
the  phenols  may  be  best  learned  by  a  study  of  the  first  member 
of  the  group.  All  the  phenols  have  names  ending  in  "ol." 

Phenol,  C6H5.OH,  was  discovered  in  coal  tar  in  1834,  and 

327 


328  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

is  to-day  one  of  the  most  important  of  the  immediate  products  of 
the  coal  tar  industry.  In  the  form  of  the  sodium  salts  of  their 
sulphuric  acid  esters,  phenol  and  several  other  members  of  this 
group  occur  in  considerable  amounts  in  the  urine  of  herbivora. 
" Carbolic  acid,"  the  name  first  given  to  phenol,  is  still  em- 
ployed in  common  usage.  Later  it  was  called  "phenyl  hydrate" 
or  "phenic  acid"  (from  <pa£vu,  to  illuminate),  apparently 
because  of  its  appearance  as  a  by-product  in  the  making  of 
illuminating  gas.  As  has  been  noticed,  it  is  from  this  rather 
fanciful  naming  that  we  have  the  term  phenyl  for  the  benzene 
radical,  CeHs. 

Properties. — Phenol  forms  long  colorless  crystals  which  melt 
at  42°,  and  usually  become  reddish  on  exposure  to  light  and  air. 
The  boiling  point  is  183°.  It  has  a  very  characteristic  odor,  is 
highly  poisonous,  blisters  the  skin,  and  has  strong  antiseptic 
properties.  Water  dissolves  about  one-fifteenth  of  its  weight  of 
phenol  at  20°,  and  in  turn  phenol  dissolves  about  one-third  of 
its  weight  of  water.  The  presence  of  water  in  phenol  lowers  its 
melting  point,  so  that  even  small  amounts  of  water  cause  it  to 
remain  liquid  at  and  below  the  ordinary  temperature.  Phenol 
was  formerly  much  used  in  surgery  as  an  antiseptic,  and  is  em- 
ployed in  the  preparation  of  picric  acid,  dyes,  and  some  medicines. 

Chemically,  phenol  acts  as  a  weak  acid  whose  salts  are  de- 
composed at  ordinary  temperatures  by  carbonic  acid — though 
carbon  dioxide  is  evolved  when  sodium  carbonate  is  brought 
into  boiling  phenol.  In  both  phenol  and  alcohols  the  hydrogen 
of  the  hydroxyl  group  can  be  replaced  by  metals,  but  the 
"phenolates"  are  more  salt-like  in  character  than  the  alcohol- 
ates.  The  latter  are  at  once  decomposed  by  water,  and  conse- 
quently, alcohols  insoluble  in  water  (i.e.,  amyl  alcohol),  do  not  dis- 
solve in  aqueous  solutions  of  alkalies.  Phenolates  are  more 
stable,  and  phenol  dissolves  freely  in  alkaline  solutions.  The 
weakness  of  the  acid  character  of  phenol  is  shown,  however,  by 
the  alkaline  reaction  of  solutions  of  the  alkali  phenolates.  The 


PHENOLS — AROMATIC    ALCOHOLS — ETHERS  329 

acid  properties  of  phenol,  like  the  absence  of  alkalinity  in  the  aro- 
matic amines  is  evidence  of  the  essentially  negative  character  of 
phenyl.  When  this  negative  character  is  increased  by  the  intro- 
duction of  negative  atoms  or  groups  into  the  phenyl  radical,  the 
acidity  becomes  much  more  pronounced;  trinitrophenol,  for 
example,  is  a  comparatively  strong  acid,  and  is  called  picric  acid. 
Reactions. — i.  Phenol  reacts  like  an  alcohol  with:  (a)  Metals, 
forming  salts,  phenolates.  (b)  Acyl  chlorides,  to  form  esters: 

C6H5.OH  +  CH3.CO.C1  =  C6H5O.OC.CH3  +  HC1 

Phenol  Acetyl  chloride  Phenyl  acetate 

Nitric  and  sulphuric  acid  esters  are  not  formed,  as  with  alcohols, 
by  the  direct  action  of  these  acids  on  phenol,  nitro  or  sulphonic 
acid  substitution  products  being  produced  instead.  Phenyl- 
sulphuric  acid  in  the  form  of  its  potassium  salt  can,  however,  be 
obtained  by  warming  a  concentrated  solution  of  potassium 
phenolate  with  potassium  pyrosulphate: 

C6H5OK  +  K2S207  =  C6H6O.S02.OK  +  K2S04 

But  on  heating  this  salt  in  the  dry  state,  it  suffers  molecular  re- 
arrangement into  KO.SO2.CeH4.0H,  the  potassium  salt  of 
phenolsulphonic  acid. 

(c)  With  alkyl  halides  the  alkali  salts  of  phenol  form  mixed 
aryl-alkyl  ethers  (cf.  p.  74): 

C6H5.ONa  +  CH3I  =  C6H5.OCH3  +  Nal 

Sodium  Anisol 

phenolate 

(d)  With  phosphorus  pentachloride  or  bromide  the  hydroxyl 
group  is  replaced  by  chlorine  or  bromine.     But  this  reaction  is 
not  very  satisfactory  as  the  yield  of  chlor  or  brombenzene  is  small, 
various  other  compounds  being  formed  at  the  same  time. 

2.  Unlike  alcohols,  phenol  is 

(a)  Reduced  to  the  corresponding  hydrocarbon  (benzene)  by 
distillation  with  zinc  dust. 


330  INTRODUCTION  TO   ORGANIC  CHEMISTRY 

(b)  Changed  to  an  amine  (aniline)  by  heating  with  ammonia 
in  the  presence  of  zinc  chloride. 

(c)  In  the  form  of  alkali  phenolate,  it  is  converted  by  carbon 
dioxide  into  the  unstable  salt  of  the  carbonic  acid  ester: 

C6H6.ONa  +  CO2  =  C6H5.O.CO.ONa 

This  sodium  phenyl  carbonate,  on  heating  under  pressure,  under- 
goes a  molecular  rearrangement  into  the  salt  of  hydroxybenzoic 
or  salicylic  acid,  HO.C6H4.CO.ONa  (i,  2);  hence  this  reaction 
gives  a  means  for  making  hydroxy  acids  from  phenols  (cf.  p.  362). 

3.  Phenol  is  more  easily  oxidized  than  benzene.     As  the  car- 
bon atom  to  which  the  hydroxyl  is  united  is  not  combined  with 
hydrogen  atoms,  phenol  is  analogous  to  a  tertiary  alcohol  and 
cannot  yield  aldehydes  or  acids  on  oxidation.     Under  certain 
conditions  the  dihydric  phenols,  catechol,  and  quinol  are  formed, 
but  the  oxidation  products  are,  in  general,  quite  various,  including 
both  simpler  and  more  complex  compounds. 

4.  The  hydrogen  of  the  phenyl  group  is  rendered  particularly 
reactive  by  the  presence  of  the  hydroxyl  group.    Tribrom  and 
trinitrophenol  and  phenoltrisulphonic  acid   are   readily  formed 
by  the  direct  action  of  bromine,  nitric  or  sulphuric  acids. 

Dilute  aqueous  solutions  of  phenol  give  a  violet  color  with 
ferric  chloride,  and  bromine  water  precipitates  yellowish  tribrom- 
phenol.  These  reactions  do  not  serve,  however,  to  identify  phenol, 
since  other  members  of  this  group  and  some  other  substances  show 
a  similar  behavior. 

Formation  of  Phenols. — The  hydroxyl  group  can  be  introduced 
(a)  in  place  of  the  sulphonic  acid  group  by  melting  the  com- 
pound with  solid  alkali  (pp.  290,  334).  This  is  the  method  used 
in  the  commercial  production  of  phenol,  (b)  In  place  of  the  amino 
group  by  the  diazo  reaction  (p.  315).  Phenols  can  also  be  pre- 
pared (c)  from  hydroxy-acids  by  replacement  of  the  carboxyl 
group  with  hydrogen,  through  fusion  with  sodium  hydroxide  or 
lime  (p.  274);  and  (d)  by  means  of  the  Grignard  reagents  (p.  37). 


PHENOLS — AROMATIC   ALCOHOLS — ETHERS 


331 


Name 
Phenol 

o-Cresol 

m-Cresol 

p-Cresol 

Carvacrol 

Thymol 

Pyrocatechol 

Resorcinol 

Quinol  (hydroquinone) 

Pyrogallol 

Phloroglucinol 

Hexahydroxybenzene 

Sym.-tribromphenol 
o-Phenolsulphonic  acid 
o-Nitrophenol 

p-Nitrophenol 

Sym.-trinitrophenol 

(picric  acid) 

o-Aminophenol 


PHENOLS  AND  SUBSTITUTED  PHENOLS 

Formula 
C6H6OH 


Melting 
point 


/CH3  (i) 
CeH4\OH    (2) 

/CH3  (i) 
lH4\OH   (3) 

/CH3  (i) 
CeH4\OH    (4) 

/CH3  (i) 
C6H3^OH    (2) 

\CH.(CH3)2(4) 


(i) 

^CHtCHs),  (4) 

C6H4(OH)2  (i,  2) 
C6H4(OH)2  (i,  3) 
C6H4(OH)2  (i,  4) 
C6H3(OH)3  (i,  2,  3) 
C6H3(OH)3  (i,  3,  5) 
C6(OH)6 

/OH  (i) 
5H2\Br3  (2,  4,  6) 

/OH  (i) 
H4\S03H  (2) 

/OH   (i) 
CeH4\N02  (2) 

/OH   (i) 

C6H4\N02(4) 

/OH  (i) 
2\(N02)3(2,  4,  6) 

/OH   (i) 
UH4\NHa(2) 


42.5 


30 


36° 


104 
in 
169 
132 
219 


92 

44-3 
114° 

112.5° 
170° 


Boiling 
point 

181.5 
1 88° 
200.5° 


2371 


232^ 


240° 
276. Sc 
285° 


214 


332  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

Homologues  of  Phenol 

Among  the  phenols  containing  a  single  hydroxyl  group,  the 
following  are  of  especial  importance  and  serve  as  types  of  the 
homologues  of  phenol. 

Cresols,  CH3.C6H4.OH.  All  three  of  the  isomeric  cresols  are 
obtained  among  the  products  of  the  distillation  of  coal  tar  and 
of  beech  wood.  The  separation  of  the  three  cresols  by  distilla- 
tion is  difficult  because  of  the  nearness  of  their  boiling  points 
(see  table),  but  sometimes  the  ortho  cresol  is  thus  isolated  from 
the  other  two.  They  .can  be  prepared  in  pure  form  from  the 
corresponding  toluenesulphonic  acids,  or  from  the  toluidines  by 
the  diazo  reaction.  Meta  cresol  can  also  be  made  by  heating 
thymol  with  phosphorus  pentoxide: 

/CH3   (i)  P2o6  /CH3  (i) 

C6H3A)H     (3)     =   C6H<  +C3H6 

\C3H7(4)  XOH   (3) 

Thymol  Meta  cresol  Propylene 

This  reaction  by  which  a  long  side-chain  is  replaced  by  hydrogen 
with  the  formation  of  an  olefine  can  be  applied  in  making  other 
phenols. 

The  cresols  resemble  phenol  in  most  of  their  properties.  They 
are  more  strongly  antiseptic  than  phenol,  and  the  crude  mixture  of 
them  from  coal  tar  is  used  for  disinfecting  purposes.  They  give 
a  bluish  coloration  with  ferric  chloride.  It  is  a  curious  fact  that 
the  hydroxyl  group  in  cresols  protects  the  methyl  group  from 
oxidation  by  chromic  acid.  This  is  also  the  case  with  similar 
phenols.  If,  however,  the  hydrogen  of  the  hydroxyl  group  is 
replaced  by  an  alkyl  or  acyl  group,  oxidation  occurs. 

/CH3   (i)  /CH3   (i) 

Carvacrol,  C6H3^-OH     (2),  and  Thymol,  C6H3^-OH    (3), 

\C3H7  (4)  \C3H7  (4) 

are  the  two  possible  monohydric  phenol  derivatives  of  cymene 


PHENOLS — AROMATIC   ALCOHOLS — ETHERS  333 

(p.  278).  Both  of  them  occur  in  a  number  of  essential  vegetable 
oils,  and  are  obtained  from  these  sources.  The  positions  of  the 
hydroxyl  group  with  reference  to  the  methyl  group  is  proved 
by  the  conversion  of  carvacrol  into  o-cresol,  and  of  thymol  into 
m-cresol,  when  they  are  heated  with  phosphorus  pentoxide. 
Carvacrol  can  be  prepared  by  heating  camphor  with  iodine,  or 
made  from  cymenesulphonic  acid.  Thymol  is  made  commercially 
from  the  oil  of  thyme  where  it  exists  together  with  cymene,  by 
shaking  the  oil  with  caustic  soda.  It  has  a  thyme-like  odor,  is 
very  sparingly  soluble  in  water,  and  is  not  poisonous  like  phenol 
and  the  cresols.  It  finds  employment  in  medicine  as  an  anti- 
septic. Carvacrol  is  colored  green  by  ferric  chloride,  but  thymol 
gives  no  coloration. 

As  an  illustration  of  a  phenol  with  an  unsaturated  side  chain 
may  be  noted  chavicol,  p-allylphenol,  HO.C6H4.CH2.CH:CH2, 
which  occurs  in  the  betel  leaves  that  are  chewed  by  natives 
in  the  East. 


Phenols  with  More  Than  One  Hydroxyl  Group 

The  polyhydric  phenols  differ  from  the  simpler  phenols  chiefly 
in  their  greater  solubility  in  water  and  in  the  fact  that  most  of 
them  are  strong  reducing  agents.  Several  of  them  are  found  in 
wood  tar,  especially  in  the  form  of  their  methyl  ethers.  They 
can  be  made  by  the  usual  methods  for  introducing  hydroxyl  groups. 
Their  behavior  in  some  particulars  depends  markedly  on  the 
relative  positions  of  the  hydroxyl  groups. 

Catechol,  or  pyrocatechol,  C6H4(OH)2  (i,  2),  is  named  from 
catechu,  a  product  from  certain  Indian  trees,  having  been  first 
made  by  the  dry  distillation  of  this  substance.  It  can  be  made 
by  the  usual  synthetical  methods,  but  is  conveniently  prepared 

yOCHa 

from  its  methyl  ether,  guaiacol,  C6H4<f  ,  which  is  obtained 

XOH 


334  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

from  wood  tar.  Catechol  is  readily  soluble  in  water.  It  is  a 
stronger  reducing  agent  than  either  of  its  two  isomers.  An 
alkaline  solution  absorbs  oxygen  from  the  air  and  turns  green  and 
then  black.  Catechol  in  aqueous  solution  gives  a  green  color 
with  ferric  chloride,  which  turns  violet  on  addition  of  a  solution 
of  sodium  carbonate  or  acetate.  This  reaction  is  characteristic 
for  aromatic  orthodihydroxyl  compounds. 

Resorcinol,  C6H4(OH)2(i,  3),  derives  its  name  from  the  related 

yCH3  (i) 
and  previously  known  substance  orcin  C6H3^  which 

\OH),  (3,  5) 

in  turn  was  named  from  its  discovery  in  the  investigation  of  the 
so  called  "lichen  orcina."  Resorcinol  is  formed  by  melting  ben- 
zenedisulphonic  acids,  halogen-benzenesulphonic  acids,  or  halo- 
gen-phenols with  potassium  hydroxide.  Many  ortho  and  para 
compounds  of  these  classes,  as  well  as  the  meta  compounds,  yield 
in  this  way  the  meta  compound  resorcinol.  Two  things  are  to 
be  noted  in  this  connection:  That  halogen  atoms  when  sub- 
stituted in  phenols  can  be  replaced  by  hydroxyl  directly,  and 
second,  that  in  the  transformations  of  ortho  and  para  compounds 
given  above  the  relative  positions  of  groups  are  changed,  the 
greater  stability  of  the  meta  configuration  usually  determining 
the  final  result.  Reactions  of  this  character  evidently  cannot  be 
employed  for  the  determination  of  position. 

Resorcinol  is  prepared  industrially  from  benzene-m-disulphonic 
acid.  It  gives  a  dark  violet  with  ferric  chloride,  which  disap- 
pears on  addition  of  sodium  acetate  (compare  with  catechol). 
When  it  is  heated  with  phthalic  anhydride  (p.  369)  and  the 
product  is  dissolved  in  dilute  sodium  hydroxide,  the  yellow  solu- 
tion shows  a  beautiful  green  fluorescence.  Other  meta  diphenols 
give  this  reaction,  which  may  therefore  serve  as  a  test  for  these 
compounds,  and  also  for  certain  dicarboxylic  acids,  like  phthalic 
acid. 

Resorcinol  is  largely  used  in  making  the  dyes  fluoresce'in  and 
eo sin  (p.  370),  other  phthalem  dyes,  and  certain  azo  colors. 


PHENOLS  —  AROMATIC   ALCOHOLS  —  ETHERS  335 

Quinol,  or  hydroquinone,  CeH4(OH)2  (i,  4),  so-called  because 
first  obtained  by  the  dry  distillation  of  quinic  acid  CeHXOH)^- 
CO.OH  (p.  375),  occurs  in  the  leaves  of  the  bearberry  as  a  gluco- 
side.  It  is  usually  prepared  by  reducing  quinone  CeH4O2  (p.  350) 
by  sulphurous  acid.  With  ferric  chloride  quinol  gives  a  dark 
green  solution  which  turns  yellow  from  its  oxidation  to  quinone  : 


C6H4(OH)2  +  O  =  C6H4O2  +  H2O 

Quinol  Quinone 

Other  mild  oxidizing  agents  effect  the  same  change,  and  this  reac- 
tion is  characteristic  of  quinol  and  its  homologues,  the  p-dihydric 
phenols  or  hydrochinones  —  which  are  thus  converted  into  the 
corresponding  yellow  quinones. 

The  three  isomeric  dihydric  phenols  are  colorless  crystalline 
substances.  The  solubility  of  resorcinol  is  the  greatest  and  that  of 
quinol  the  least  (5.85:100  at  15°).  The  melting  points  increase 
from  catechol  to  quinol;  and  in  reducing  power  quinol  lies  between 
the  other  two.  Cathechol  and  quinol  are  used  as  developers  in 
photography. 

Pyrogallol,  or  pyrogallic  acid,  C6H3(OH)3  (i,  2,  3),  is  prepared 
by  heating  gallic  acid  (p.  366): 

(OH)3C6H2.CO.OH  =  C6H3(OH)3  +  CO2 

Gallic  acid  Pyrogallol 

It  forms  colorless  crystals  which  dissolve  in  about  two  parts 
of  water.  Its  alkaline  solutions  absorb  oxygen  rapidly  from  the 
air  or  other  gaseous  mixtures  and  turn  dark  brown.  On  ac- 
count of  this  property  pyrogallol  solutions  are  used  in  the  analysis 
of  gases.  This  behavior  marks  it  as  an  energetic  reducing  agent. 
It  precipitates  gold,  silver,  and  mercury  from  solutions  of  their 
salts,  and  is  extensively  used  as  a  photographic  developer. 
Among  the  oxidation  products  of  pyrogallol  which  are  formed 
in  these  reductions  of  other  substances,  are  acetic  acid  and  carbon 
dioxide. 

The  two  isomers  of  pyrogallol,  phloroglucinol  (i,  3,  5),  and 
hydroxyquinol  (i,  2,  4),  are  of  little  importance. 


33  6  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

The  three  possible  tetrahydricphenols  are  well  known,  as  such, 
or  in  the  form  of  derivatives.  Pentahydricphenols  are  unknown. 

Hexahydroxylbenzene,  C6(OH)  6,  has  been  made  synthetically. 
It  is  a  crystalline  substance  which  is  not  very  soluble  in  water  and 
very  slightly  soluble  in  alcohol  and  ether.  Its  solutions  rapidly 
become  violet-red  in  the  air,  and  reduce  silver  nitrate  instantane- 
ously in  the  cold.  With  acetic  anhydride  it  forms  a  hexa-acetyl 
derivative,  C6(O.OC.CH3)6.  The  potassium  salt  of  this  hexa- 
phenol,  Ce(OK)6,  is  formed  by  the  action  of  carbon  monoxide  on 
melted  potassium,  and  from  this  the  phenol  can  be  set  free  by 
dilute  acid.  Since  by  the  distillation  of  hexaphenol  with  zinc 
dust  benzene  is  formed,  an  interesting  synthesis  of  benzene  from 
the  elements  can  thus  be  effected.  The  potassium  compound, 
which  is  a  gray,  crystalline  substance,  acquires  in  the  air  an 
explosive  property,  which  had  to  be  reckoned  with  in  the  older 
process  for  making  potassium  (see  Inorganic  Chemistry). 

The  homologues  of  the  polyhydricphenols  are  not  important. 

Derivatives  of  Phenols 

Halogen  derivatives  of  the  phenols  are  readily  formed  by  the 
direct  action  of  chlorine  and  bromine,  and  iodine  replaces 
hydrogen  when  brought  into  an  alcoholic  solution  of  the  phenol 
in  the  presence  of  mercuric  oxide.  The  halogen  atoms  enter  in 
the  ortho  or  para  positions  relative  to  the  hydroxyl  groups.  The 
halogen  derivatives  can  also  be  made  from  the  aminophenols 
by  the  diazo  reaction. 

They  are  colorless  crystalline  substances  which  are  more 
strongly  acid  than  the  phenols.  On  melting  with  potassium 
hydroxide  the  halogen  is  exchanged  for  hydroxyl,  molecular 
rearrangement  often  occurring  in  the  reaction  with  chlor  and 
bromphenols,  so  that  p-bromphenol  yields  not  only  quinol  (1,4), 
but  considerable  amounts  of  resorcinol  (1,3). 


PHENOLS — AROMATIC  ALCOHOLS — ETHERS  337 

Phenolsulphonic  Acids. — By  the  action  of  concentrated  sul- 
phuric acid  on  phenol,  the  orthosulphonic  acid  is  the  chief  product 
in  the  cold;  but  if  the  mixture  of  acid  and  phenol  is  heated,  the 
para  compound  alone  is  formed.  The  orthosulphonic  acid  is 
unstable  when  heated,  suffering  rearrangement  into  the  para 
compound,  and  this  even  occurs  in  evaporating  its  aqueous  solu- 
tion. The  chemical  properties  of  the  phenol  sulphonic  acids  are 
those  which  are  characteristic  of  both  phenol  and  sulphonic 
acids.  Ortho  phenolsulphonic  acid  is  a  stronger  disinfectant  than 
phenol,  and  has  been  used  for  this  purpose  under  the  name  of 
"aseptol." 

Nitrophenols. — Ortho  and  para  nitrophenol  are  formed  by  the 
action  of  dilute  nitric  acid  on  phenol,  and  are  easily  separated, 
since  the  ortho  compound  alone  is  volatile  with  steam.  They 
are  both  crystalline  solids.  The  para  compound  is  not  only  non- 
volatile with  steam  but  is  colorless  and  odorless,  while  ortho 
nitrophenol  is  yellow,  and  has  a  strong  odor  resembling  that  of 
nitrobenzene.  They  are  used  industrially  in  the  preparation  of 
dyes  and  medicines.  Meta  nitrophenol  cannot  be  made  directly, 
but  is  prepared  from  m-nitraniline  by  the  diazo  reaction. 

Picric  Acid,  (i)  HO.C6H2(NO2)3(2,  4,  6),  is  symmetrical  trini- 
trophenol.  This  important  substance  is  the  end-product  in  the 
nitration  of  phenol.  It  is  usually  prepared  by  dissolving  phenol 
in  concentrated  sulphuric  acid,  then  adding  the  phenolsulphonic 
acid  to  concentrated  nitric  acid,  and  finally  heating  for  some  time 
at  100°.  On  cooling,  the  picric  acid  separates  as  in  a  mass  of 
pale  yellow  crystals.  It  dissolves  rather  slightly  in  hot  water, 
and  at  20°  its  solubility  is  1.03:100.  It  is  freely  soluble  in  alco- 
hol, ether,  etc.,  and  its  aqueous  solutions  have  a  bitter  taste,  and 
a  strong  acid  reaction.  The  presence  of  three  nitro  groups  makes 
trinitrophenol  a  stronger  acid — more  highly  ionized— than  acetic 
acid.  The  sodium  and  the  ammonium  salts  are  quite  soluble, 
but  the  potassium  salt  dissolves  very  slightly.  With  many  hy- 
drocarbons, such  as  naphthalene  and  anthracene,  picric  acid  forms 


338  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

crystalline  molecular  compounds  well  suited  for  the  separation 
and  the  identification  of  these  hydrocarbons.  These  compounds 
are  resolved  into  their  components  by  ammonia.  In  a  similar 
way  picric  acid  is  often  used  in  the  laboratory  to  precipitate  and 
purify  organic  bases  through  the  formation  of  difficultly  soluble 
salts.  Its  solutions  and  those  of  its  alkali  salts  have  a  much 
deeper  color  than  would  be  expected  from  the  appearance  of  the 
crystals.  Picric  acid  is  a  substantive  dye  for  wool  and  silk  and 
is  largely  used,  especially  in  mixture  with  other  dyes.  It  is  the 
oldest  of  the  manufactured  organic  dyes. 

Picric  acid  is  detonated  by  mercury  fulminate  or  guncotton,  but 
does  not  explode  when  struck.  Its  alkali  and  other  salts,  however, 
explode  violently  on  percussion,  or  when  heated,  and  are  used 
in  various  explosives  (e.g.,  "melinite"). 

Dinitrocresols,  CH3.C6H2.(NO2)2.OH,  were  formerly  used  in 
the  form  of  alkali  salts  for  dyes,  under  the  names  of  "Victoria 
yellow,"  etc. 

Aminophenols  can  be  made  by  reduction  of  nitrophenols.  Of 
especial  interest  is  their  formation  by  molecular  rearrangement 
of  aromatic  hydroxylamines  (p.  321).  In  consequence  of  this 
reaction  many  aminophenols  are  conveniently  prepared  from 
nitro  compounds  by  electrolytic  reduction.  Thus,  from  nitro- 
benzene dissolved  in  sulphuric  acid,  p-aminophenol  is  prepared: 

CeHsNOs,  +  4H  ->  CeHs.NH.OH  ->  HO.CeKU.NH-, 

The  aminophenols  are  basic  through  the  presence  of  the 
amino  group  and  form  stable  salts  with  acids;  and  the  acidity 
of  tfre  hydroxyl  group  is  so  weakened  that  although  they  dissolve 
in  caustic  alkalies,  they  do  not  form  definite  alkali  salts. 

The  aminophenols  are  mostly  quite  soluble  in  water,  and  their 
solutions  oxidize  in  the  air  and  consequently  are  reducing  agents. 
A  number  of  them  are  employed  as  photographic  developers: 
"Rodinal"  is  the  hydrochloric  acid  salt  of  p-aminophenol; 
"Amidol"  a  salt  of  o-p-diaminophenol;  "Reducin,"  a  salt  of  di- 


PHENOLS — AROMATIC   ALCOHOLS — ETHERS  339 

ortho-para  triaminophenol;  and  "Metol,"  the  sulphate  of  methyl- 
aminophenol, 

C6H4(OH)NH(CH3). 

Salvarsan,  or  606,  recently  introduced  into  medicine  as  a  speci- 
fic for  syphilis,  is  the  dihydrochloride  of  a  derivative  of  amino- 
phenol  containing  arsenic, 

As  -  C6H3(NH2)OH 

I 
As  -  C6H3(NH2)OH 

Esters  of  Phenols. — Of  these  only  certain  phenylsulphuric 
acids  need  be  mentioned,  which  occur  as  sodium  salts  in  urine. 

Bakelite. — By  a  "condensation"  of  phenols  and  formaldehyde 
under  certain  conditions,  a  hard,  infusible  product  is  obtained, 
which  under  the  name  of  "  bakelite  "  is  finding  many  applications. 
It  resembles  amber  in  appearance,  burns  with  difficulty,  is  insoluble 
in  all  solvents  and  withstands  almost  all  chemical  reagents.  If 
made  from  phenol  its  formula  is  represented  by  C43H38O7,  and 
it  has  received  the  chemical  name  of  oxybenzylmethylene- 
glycolanhydride.  In  the  form  of  a  transition  product  it  is 
softened  by  heat  and  can  be  molded.  It  is  mostly  used  com- 
pounded with  other  substances  such  as  wood  pulp,  for  the 
manufacture  of  a  great  variety  of  articles  for  which  celluloid, 
hard  rubber,  and  amber  have  been  employed,  for  insulating 
purposes,  etc. 

Aromatic  Alcohols 

The  aromatic  compounds  which  contain  hydroxyl  in  a  side 
chain  can  be  made  by  the  synthetic  methods  employed  for  the 
preparation  of  the  aliphatic  alcohols.  When  the  corresponding 
aldehydes  are  available,  as  in  some  cases,  the  primary  alcohols 
are  conveniently  prepared  from  them  by  the  usual  methods  of 
reduction,  or  by  shaking  the  aldehyde  with  an  aqueous  solution 
of  an  alkali.  Aliphatic  aldehydes  (except  formaldehyde)  are 


340  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

converted  into  resins  by  alkalies,  but  aromatic  aldehydes  undergo 
a  reaction  of  a  different  nature  in  which  one  half  of  the  aldehyde  is 
reduced  to  alcohol  and  the  other  half  oxidized  to  an  acid  (salt) 
(cf.  p.  84): 


KOH  =  C6H6.CH2OH  +  C6H5.CO.OK 

Benzaldehyde  Benzyl  alcohol  Potassium  benzoate 

Alcohols  in  which  the  group  —  CH2OH  is  directly  united  to 
ring  carbon  can  also  be  obtained  by  reduction  of  the  correspond- 
ing acid  amides  : 

CeH6.CO.NH2  +  4H  =  C6H6.CH2OH  +  NH3 

The  aromatic  alcohols  completely  resemble  the  aliphatic  alco- 
hols, and  differ  from  the  phenols  in  the  greater  readiness  with  which 
they  form  esters,  and  are  oxidized  to  aldehydes,  acids  or  ketones, 
as  well  as  by  the  fact  that  they  do  not  form  stable  salts  with 
bases. 

Benzyl  Alcohol,  C6H5.CH2OH  (phenylcarbinol),  occurs  as 
benzoic  and  cinnamic  esters  in  the  balsams  of  Peru  and  Tolu,  and 
in  liquid  storax.  It  is  a  liquid  of  faint  aromatic  odor,  boiling 
at  204°.  On  oxidation  it  gives  benzaldehyde  and  benzoic  acid 
and  it  can  be  reduced  to  toluene.  Benzyl  alcohol  may  be 
considered  as  methyl  alcohol  in  which  one  hydrogen  atom  of  the 
CH3  group  is  replaced  by  phenyl.  If  two  of  these  atoms  are  thus 
replaced  the  compound  is  diphenylcarbinol  (or  benzhydrol) 
(CeHs^CHOH,  a  secondary  alcohol.  This  alcohol  may  be 
made,  like  the  secondary  alcohols  of  the  aliphatic  series,  by 
reduction  of  the  corresponding  ketone,  benzophenone  or  diphenyl- 
ketone  C^.CO.CeHs.  It  is  a  solid,  melting  at  68°  and  boiling 
at  298°.  Triphenylcarbinol,  (CeHs^COH,  is  a  tertiary  alcohol, 
which  can  be  obtained  by  the  oxidation  of  triphenylmethane, 
(C6H5)3CH,  a  reaction  peculiar  to  aromatic  compounds.  It  is 
a  solid,  melting  at  159°. 

Cinnamyl  Alcohol,  C6H5.CH:CH.CH2OH,  (7-phenyl-allyl  alco- 
hol), occurs  in  storax  as  the  ester  of  cinnamic  acid,  and  serves  as 
an  illustration  of  an  unsaturated  aromatic  alcohol.  It  melts  at 


PHENOLS — AROMATIC  ALCOHOLS — ETHERS  341 

33°,  boils  at  254°,  and  has  the  odor  of  hyacinths.  It  may  be 
reduced  to  phenylpropyl  alcohol,  C6H5.CH2.CH2.CH2OH,  and 
when  oxidized  gives  cinnamic  aldehyde,  CeHs.CHiCH.CHO,  cin- 
namic  acid,  CeHs.CHrCH.CO.OH,  or  benzoic  acid,  CeHs.CO.- 
OH  according  to  the  oxidizing  agent  employed. 

Phenol-Alcohols. — Certain  compounds  which  are  hydroxy  aro- 
matic alcohols,  or  phenol-alcohols,  since  they  contain  hydroxyl 
both  in  the  ring  and  in  a  side  chain,  occur  as  glucosides  in 
nature.  The  simplest  of  these  is  o-hydroxybenzylalcohol,  or 
salicyl  alcohol,  HO.CeH^.CH^OH,  whose  glucoside  is  salicin  which 
is  found  in  the  bark  of  the  willow.  The  alcohol  can  be  obtained 
by  splitting  off  the  sugar  of  the  glucoside  with  mineral  acids  or 
emulsin.  Salicyl  alcohol  melts  at  86°,  and  is  quite  soluble  in 
water.  It  gives  a  blue  color  with  ferric  chloride,  and  it  shows  both 
phenol  and  alcohol  reactions. 

Aromatic  compounds  containing  sulphur  in  place  of  oxygen 
can  be  prepared,  but  these  thiophenols,  aromatic  mercaptans, 
thioethers,  etc.,  present  no  very  important  points  of  interest. 

Aromatic  Ethers 

Diphenyl  Ether,  C6H5.O.C6H5,  is  the  simplest  ether  contain- 
ing two  aryl  groups.  It  can  be  made  by  heating  phenol  with 
anhydrous  zinc  chloride,  or  by  the  dry  distillation  of  aluminium 
phenolate,  A1(O.C6H6)3.  It  has  a  geranium-like  odor,  and 
melts  at  28°  and  boils  at  252°. 

Anisol,  CeHs.OCHs,  phenyl-methyl  ether,  is  produced  by  dis- 
tilling anisic  acid,  CO.OH.C6H4.OCH3  (which  is  obtained  by 
oxidation  of  anethol,  the  chief  constituent  of  anise  oil)  with  lime, 
or  by  heating  guaiacol  with  zinc  dust.  .  Anisol,  and  other  ethers 
of  this  type,  can  be  made  by  the  action  of  alkali  phenolates  on 
alkyl  halides: 

C6H6.ONa  +  CH3I  =  C6H5.OCH3  +  Nal 
Their  formation  from  aryl  halides  and  sodium  alkoxides  is  also 
possible,  but  more  difficult,  because  of  the  smaller  reactivity  of 
the  halogen  atom  when  united  to  a  cyclic  radical. 


34 2  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

Guaiacol,C6H4(OH)(OCH3)(i,2),  was  first  obtained  from  gum 
guaiacum.  It  is  among  the  products  of  wood  tar,  and  can  be 
made  from  catechol  (p.  333)  of  which  it  is  the  methyl  ether. 

Eugenol,  or  allyl-guaiacol,  C6H3(OH)(OCH3)(CH2.CH:CH2) 
(i,  2,  4),  occurs  in  oil  of  cloves  which  is  obtained  by  distilling 
cloves  with  steam,  and  in  other  essential  oils.  In  oil  of  cloves 
it  is  associated  with  a  terpene  of  the  formula,  Ci5H24,  and  it  is 
separated  from  this  as  an  alkali  salt  by  its  solubility  in  an 
alkaline  solution.  It  has  a  strong  odor  of  cloves,  and  unites  the 
properties  of  a  phenol,  an  ether  and  an  unsaturated  compound. 
It  is  a  colorless  oil  which  boils  at  247°,  and  is  used  for  perfumery 
and  for  making  vanillin  (p.  347). 

Safrol,  the  chief  constituent  of  sassafras  oil,  has  the  constitution, 

O 

CH2:CH.CH2.C6H3<^>CH2  (i,  3,  4) 
O 

which  is  that  of  methylene  ether  of  propylene  dihydroxybenzene. 
It  is  very  poisonous,  but  has  been  used  to  cover  the  unpleasant 
fatty  odor  of  soaps.     It  also  serves  for  the  preparation  of  pipero- 
O 


nal,   CHO.C6H3<    >CH2,  the   methylene   ether   of   dihydroxy- 

O 

benzaldehyde  (i,  3,  4)  which  is  a  product  of  its  oxidation;  and  is 
employed,  on  account  of  its  heliotrope  odor,  in  perfumery  under 
the  name  of  "heliotropin."  Safrol  melts  at  8°  and  boils  at 
232°,  piperonal  at  37°  and  263°. 

Phenacetin,  the  well-known  drug,  is  an  ethereal  derivative 
of  p-hydroxyacetanilide,  having  the  formula,  C6H4(OC2H5)- 
(NH.OC.CH3)  (1,4).  It  forms  colorless  crystals  which  melt  at 
135°,  and  is  very  slightly  soluble  in  cold  water.  It  is  made  by 
boiling  the  ethyl  ether  of  p-aminophenol  with  glacial  acetic  acid. 


CHAPTER  XXVI 
AROMATIC  ALDEHYDES,  KETONES  AND  QUINONES 

Aldehydes 


The  aldehyde  group,  —  C\      ,  requiring    two  valencies  for 

oxygen  and  one  for  hydrogen,  cannot  be  developed  on  nucleus 
carbon.  The  aromatic  aldehydes  are,  therefore,  compounds  in 
which  this  group  is  directly  or  indirectly  united  to  an  aryl  radical 
in  place  of  hydrogen.  There  are  thus  two  varieties  of  aromatic 
aldehydes,  both  of  which  may  be  regarded  as  aliphatic  alde- 
hydes in  which  aryl  groups  have  been  substituted  for  hydrogen 
in  formaldehyde,  or  in  the  radicals  of  higher  aldehydes. 

Preparation.  —  Aromatic  aldehydes  can  be  made  from  the 
alcohols,  as  in  the  case  of  formaldehyde  and  acetaldehyde,  but 
the  corresponding  alcohols  are  generally  not  readily  accessible. 
In  the  aromatic  series,  as  we  have  seen,  the  hydrocarbons  form  the 
most  important  sources  for  the  preparation  of  other  compounds, 
hence  a  method  much  employed  for  making  aldehydes  which 
have  the  aldehyde  group  immediately  attached  to  the  benzene 
ring,  is  by  first  forming,  directly  from  the  hydrocarbons,  deriva- 
tives having  chlorine  in  a  side  chain,  and  then  converting  the  alkyl 
halogen  group  into  the  aldehyde  group.  In  this  way  benzalde- 
hyde  is  prepared  commercially  from  toluene.  The  toluene  is 
chlorinated  with  the  production  of  benzalchloride,  CeHs.CHC^, 
as  the  chief  product,  and  then  the  chlorine  is  replaced  by  oxygen 
by  heating  under  pressure  with  milk  of  lime: 


C6H6.CHC12  +  Ca(OH)2  =  CeHs.CHO  +  CaCl2  +  H2O 

343 


344  INTRODUCTION    TO    ORGANIC    CHEMISTRY 

The  reaction  can  be  effected  with  other  agents,  even  with  water. 

Benzaldehyde  may  also  be  made  from  benzylchloride,  CeHs.- 
CH2C1,  by  oxidation  with  lead  or  copper  nitrate;  or  direct  from 
toluene  by  an  oxidation  effected  by  chromyl  chloride,  CrO2Cl2 
(Etard's  method).  This  method  of  oxidizing  a  methyl  group  to 
an  aldehyde  group  may  also  be  used  for  the  preparation  of  other 
aromatic  aldehydes. 

The  aldehyde  group  may  also  be  introduced  in  place  of  a 
hydrogen  atom  of  the  aryl  nucleus  by  Gattermann's  reaction. 
Thus  benzaldehyde  is  prepared  directly  from  benzene  by  passing 
into  it  a  mixture  of  hydrogen  chloride  and  carbon  monoxide  in 
the  presence  of  anhydrous  cuprous  chloride  and  aluminium 
chloride.  It  may  be  assumed  that  the  unstable  formyl  chloride, 
HCO.C1  is  an  intermediate  product: 


+  HCO.C1  =  CeHB.CHO  +  HC1 

Aldehydes,  in  which  the  aldehyde  group  is  linked  to  the  cyclic 
radical  by  other  groups,  are  made  by  distillation  of  a  mixture  of 
calcium  formate  and  the  calcium  salt  of  the  corresponding  acid  — 
a  general  method  for  both  aliphatic  and  aromatic  aldehydes: 
C6H5.CH2.CO.Oca  +  H.CO.Oca  =  C6H5.CH2.CHO  +  CaCO3 
Properties.  —  The  aromatic  aldehydes  are  very  like  the  ali- 
phatic aldehydes  in  behavior,  but  differ  from  these  in  some 
respects.  They  form  no  addition  products  with  ammonia,  though 
they  unite  with  acid  sodium  sulphite  and  hydrocyanic  acid;  they 
do  not  reduce  Fehling's  solution,  though  ammoniacal  silver 
nitrate  is  reduced;  and  they  do  not  polymerize  in  the  manner 
characteristic  of  the  aliphatic  aldehydes,  or  form  resins  when 
treated  with  caustic  alkalies.  With  ammonia,  they  form  con- 
densation products  such  as  hydrobenzamine,  (C6H5.CH3)N2, 
from  benzaldehyde,  resembling  in  this  respect  formaldehyde 
(p.  84);  and  again  like  formaldehyde,  they  are  converted  by 
concentrated  alkalies  into  a  mixture  of  the  corresponding  alcohol 
and  the  alkali  salt  of  the  corresponding  acid: 


AROMATIC   ALDEHYDES  345 

2C6H5.CHO  +  KOH  =  C6H5.CH2OH  +  C6H5.CO.OK 

Benzaldehyde  Benzyl  alcohol  Potassium  benzoate 

With  chlorine  the  aromatic  aldehydes,  unlike  the  aliphatic 
aldehydes,  yield  the  corresponding  acid  chlorides  (cf.  p.  358);  but 
like  the  aliphatic  aldehydes  they  form  hydrazones  with  phenyl- 
hydrazine  (cf.  p.  80). 

Although  the  aldehyde  group  is,  in  general,  readily  oxidized 
to  the  carboxyl  group,  aromatic  aldehydes  can  be  successfully 
nitrated  without  such  oxidation  by  working  at  temperatures 
below  o°. 

Aromatic  aldehydes  form  condensation  products  with  many 
varieties  of  aliphatic  and  aromatic  compounds,  the  combina- 
tion taking  place  with  the  loss  of  the  elements  of  water,  thus-. 

C6H5.CHO  +  2C6H6.CH3  =  C6H5.CH(C6H4.CH3)2  +  H2O 
C6H5.CHO  +  CH3.CO.ONa  =  C6H5.CH:CH.CO.ONa  +  H2O 

Benzaldehyde,  C6H5.CHO,  is  one  of  the  products  of  the 
hydrolysis  of  amygdaline,  a  glucoside  which  is  present  in  bitter 
almonds  and  the  kernels  of  other  fruits,  hydrocyanic  acid  and 
glucose  being  formed  at  the  same  time.  Some  of  the  many 
methods  proposed  for  its  commercial  preparation  have  been  de- 
scribed above.1  It  is  commonly  called  "oil  of  bitter  almonds," 
and  is  used  for  flavoring,  and  for  making  dyes. 

Benzaldehyde  is  a  colorless  oil  which  boils  at  179°  and  is 
slightly  heavier  than  water.  It  is  very  easily  oxidized  to  benzoic 
acid,  the  change  taking  place  slowly  in  contact  with  air.  In 
the  atmospheric  oxidation  of  benzaldehyde  it  has  been  found 
that  an  intermediate  product,  benzoyl-hydrogen  peroxide, 


is  formed.     This  is  an  active  oxidizing  agent, 
X)-OH 

and  in  oxidizing  other  substances,  e.g.  unchanged  benzaldehyde, 
is  itself  reduced  to  benzoic  acid.  This  conversion  of  half  of  the 
absorbed  oxygen  to  the  " active"  state  is  observed  in  the  atmos- 
pheric oxidation  of  various  other  substances  (e.g.  turpentine). 

1  For  an  account  of  the  various  methods  by  which  benzaldehyde  can  be  made 
see  Thorpe's  Dictionary  of  Applied  Chemistry. 


346  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

When  chlorine  is  led  into  benzaldehyde  it  converts  it  into 
benzoyl  chloride,  CeHs.CO.Cl.  Derivatives  which  contain  a 
halogen  atom  in  the  benzene  ring  are  made  from  the  corre- 
sponding derivatives  of  benzalchloride  (cf.  p.  288).  Sulphuric 
and  nitric  acids  act  on  benzaldehyde  with  the  formation  of  the 
meta  sulphonic  acid  and  meta  nitrobenzaldehyde. 

The  only  other  aromatic  aldehydes  of  special  interest  are  -the 
following : 

/CHO  (i) 

Cuminic  Aldehyde,   C6H4<(  p-isopropyl  ben- 

\CH(CH,),  (4), 

zaldehyde,  occurs  in  caraway  oil  and  other  essential  oils.  Its 
constitution  is  proved  by  its  oxidation  to  terephthalic  acid  (p. 
368).  It  can  be  obtained  from  the  essential  oils  which  con- 
tain it  by  taking  advantage  of  the  small  solubility  of  the  addition 
product  it  forms  with  acid  sodium  sulphite,  and  then  distilling 
this  product  with  a  solution  of  sodium  carbonate.  This  is  a 
general  method  for  isolating  naturally  occurring  aldehydes. 

Cinnamic  Aldehyde,  C6H5.CH:CH.CHO,  is  found  in  oil  of 
cinnamon,  oil  of  cassia,  and  other  oils,  and  can  be  isolated  by  the 
method  just  described.  It  is  formed  by  the  oxidation  of  cin- 
namyl  alcohol  (p.  340),  and  can  be  prepared  by  condensing  ben- 
zaldehyde and  acetaldehyde  (p.  82),  a  reaction  which  takes  place 
in  the  presence  of  a  dilute  solution  of  sodium  hydroxide.  Cinna- 
mic aldehyde  is  an  oil  of  aromatic  odor  which  is  volatile  with 
steam,  but  cannot  be  distilled  alone  at  ordinary  pressures  without 
decomposition. 

yCHO   (l) 

Salicylic  Aldehyde,  CeH4<Q  ,  occurs  in  the  volatile  oils 

X>H  (2) 

from  varieties  of  spiraea,  and  can  be  obtained  by  the  oxidation 
of  salicin  (a  glucoside  found  in  willow  bark)  or  salicyl  alcohol. 
It  is  prepared  by  the  action  of  chloroform  on  phenol  when  this 
is  dissolved  in  an  excess  of  potassium  hydroxide: 


AROMATIC   ALDEHYDES  347 

/CHO 

C6H6.OK  +  CHC13  +  3KOH  =  C6H4<  +  3KC1  +  2H2O. 

XOK 

This  reaction,  which  is  known  as  the  Reimer-Tiemann  reaction, 
serves  to  introduce  the  aldehyde  group  into  phenol  in  the  ortho 
and  para  positions.  Probably  an  intermediate  product  contain- 
ing the  group  —  CHC12  is  first  formed,  which  is  then  converted 
into  the  aldehyde  group,  as  in  the  making  of  benzaldehyde 
(p.  343).  Salicylic  aldehyde  is  a  pleasant  smelling  liquid  which 
boils  at  196.5°.  It  gives  an  intense  violet  with  ferric  chloride, 
and  has  the  general  properties  of  a  phenol  and  an  aldehyde,  but 
does  not  reduce  Fehling's  solution. 
Anisaldehyde  is  the  methyl  ether  of  p-hydroxybenzaldehyde, 

(i) 


X)CH3  (4) 

,CH:CH.CH3 

It  is  prepared  by  oxidation  of  anethol,  CeH^  ,  which 

XOCH3 

is  the  chief  constituent  of  oil  of  aniseed.  Anisaldehyde  has  an 
agreeable  aromatic  odor  and  is  used  in  perfumery.  It  is  an  oil 
which  boils  at  245°. 

Vanillin  is  the  principal  substance  in  the  much-used  extract  of 
vanilla  which  is  extracted  from  vanilla  beans  by  alcohol.  Its 
formula  is 

/CHO  (i) 

(3). 
(4) 


It  may  be  made  from  guaiacol  (p.  342)  by  the  Reimer-Tiemann 
reaction,  and  is  prepared  commercially  chiefly  from  eugenol 
(p.  342)  by  oxidation.  Vanillin,  thus  prepared,  has  largely  sup- 
planted the  natural  extract. 

Vanillin  forms  white  crystals  which  melt  at  81°,  and  is  sparingly 
soluble  in  cold  water.  It  has  a  strong  vanilla-like  odor  and  taste. 
Its  solutions  have  an  acid  reaction  and  are  colored  blue  by  ferric 


348  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

chloride.     If  the  solution  containing  ferric  chloride  is  heated,  a 
characteristic  white  crystalline  precipitate  is  formed. 

Aromatic  Ketones 

The  compounds  of  this  class  may  be  divided  into  two  groups: 
Those  in  which  the  ketone  group  —  carbonyl  —  unites  an  aryl 
and  an  aliphatic  radical,  and  those  in  which  two  aryl  radicals  are 
thus  linked. 

Ketones  of  both  groups  can  be  obtained  by  the  general  method 
for  making  aliphatic  ketones  —  the  distillation  of  the  calcium 
salts  of  the  corresponding  acids;  or  more  advantageously,  from 
the  aromatic  hydrocarbon  and  the  appropriate  acid  chloride  by 
the  Friedel  and  Crafts  method  (p.  274). 

Acetophenone,  CeHs.CO.CHs,  the  simplest  of  the  mixed  aryl- 
aliphatic  ketones,  will  serve  as  an  illustration  of  this  group. 
It  is  best  prepared  by  the  condensation  of  benzene  and  acetyl 
chloride  by  the  Friedel  and  Crafts  reaction  : 

Aids 

O.Cl  +  C6H6  -»CH3.CO.C6H5  +  HC1 


Acetophenone  melts  at  20.5°  and  boils  at  202°.  It  is  used 
as  medicine  under  the  name  of  "  hypnone,"  as  a  hypnotic. 

Its  general  chemical  behavior  is  like  that  of  the  aliphatic  ketones, 
but  it  does  not  unite  with  acid  sodium  sulphite.  By  reduction 
with  sodium  amalgam,  it  yields,  in  part,  methylphenyl  carbinol 
CH3.CHOH.C6H5,  a  secondary  alcohol.  When  oxidized  with 
alkaline  permanganate  it  is  converted  into  a  ketone-acid, 
phenylglyoxylic  acid,  C6H5.CO.CO.OH,  and  then  into  benzoic 
acid,  CeHs.CO.OH. 

Chlorine  under  all  conditions  (temperature,  light,  chlorine 
carriers)  acts  almost  entirely  on  the  methyl  group  with  replace- 
ment of  its  hydrogen,  and  not  on  the  phenyl  radical. 

Benzophenone,  CeHs.CO.CeHs,  the  first  of  the  diaryl  ketones, 
can  be  made  by  heating  calcium  benzoate,  (CeHs.CO.O^Ca;  or 


AROMATIC    KETONES  349 

from  benzene  and  benzoyl  chloride,  CeHs.CO.Cl  by  the  Friedel 
and  Crafts  reaction.  It  melts  at  48°  and  boils  at  306°.  Under 
certain  conditions  benzophenone  is  obtained  in  an  unstable  form 
which  melts  at  27°.  This  variety  slowly  changes  to  the  other  on 
standing,  and  in  contact  with  a  trace  of  the  stable  form  the  change 
takes  place  rapidly  with  evolution  of  heat.  This  appears  to  be  a 
case  of  allotropy  due  to  molecular  arrangement,  as  with  phos- 
phorus and  sulphur. 

Benzophenone  is  reduced  by  sodium  amalgam  to  diphenyl- 
carbinol,  (CeHs^CH.OH,  or  by  zinc  and  sulphuric  acid  to  a 
pinacom,  (C6H5)2C(OH)C(OH)(C6H5)2,  and  by  hydriodic  acid  to 
diphenylmethane,  (C  eH  5)  2CH2. 

Benzoin,  CeHs.CH.OH.CO.CeHg,  is  a  ketone-alcohol,  formed 
by  the  union  of  two  molecules  of  benzaldehyde,  which  occurs 
with  molecular  rearrangement  when  the  aldehyde  is  heated  in 
dilute  alcoholic  solution  with  potassium  cyanide: 


2C6H5.C< 

Benzaldehyde  Benzoin 

Benzoin  melts  at  137°.  In  virtue  of  the  group,  CHOH.CO, 
which  it  contains,  it  is,  like  certain  ketoses  (p.  199)  which  contain 
the  same  group,  easily  oxidized  by  Fehling's  solution  even  in 
the  cold,  and  forms  a  hydrazone  and  an  osazone  with  phenyl- 
hydrazine. 

It  is  oxidized  by  nitric  acid  to  benzil  (diphenyldiketone), 
Ce^.CO.CO.C&Hs  (melting  point  95°),  and  can  be  reduced 
by  suitable  agents  to  desoxybenzoi'n  (phenylbenzylketone), 
CeH5.CH2.CO.C6H5,  hydrobenzoin,  CeHs.CH.OH.CH.OH.CeHe, 
or  dibenzyl  C6H5.CH2.CH2.C6H5. 

Quinones 

A  considerable  number  of  para  derivatives,  such  as  diamines, 
dihydroxyl  compounds  (hydrochinones),  aminosulphonic  acids, 
phenolsulphonic  acids,  aminophenols,  when  oxidized  with  chromic 


35O  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

acid  or  certain  other  acid  oxidizing  agents,  are  converted  into 
well-crystallizing  compounds  of  an  intense  yellow  color,  and  a 
pungent,  characteristic  odor.  These  substances,  which  are  called 
quinones,  withstand  the  action  of  acid  oxidizing  agents  as  is 
evident  from  the  manner  of  their  formation,  but  are  readily  re- 
duced with  the  production  of  hydrochinones. 

Benzoquinone,  usually  called  simply  quinone,  C6H4O2,  is  the 
simplest  representative  of  the  quinones.  It  was  discovered 
in  1838  as  the  oxidation  product  of  quinic  acid,  a  by-product 
obtained  in  the  extraction  of  quinine  and  allied  alkaloids  from 
cinchona  bark. 

Structure. — Quinone  is  a  para  derivative  of  benzene,  as  its 
formation  from  many  para  compounds  and  its  relation  to  quinol 
(hydrochinone)  indicates.  It  behaves  like  a  diketone  in  forming 
both  a  monoxime  and  a  dioxime  with,  hydroxylamine;  but  on 
reduction,  the  carbonyl  groups  are  converted  into  =  C.OH  group 
(quinol)  instead  of  =  CH.OH  groups  as  in  the  case  of  ordinary 
ketones.  Further,  by  phosphorus  pentachloride,  quinone,  CeH4O2, 
is  changed  into  C6H4Cl2,  one  chlorine  atom  taking  the  place  of 
each  oxygen  atom,  instead  of  a  replacement  with  two  chlorine 
atoms,  as  in  ketones.  Two  structures  are  suggested  by  these 
reactions  which  in  the  Kekule  formulation  are: 

O 


HC         CH 

II          I 
HC        CH 


\l 


O 


and 


HC        CH 

II         II 
HC        CH 

\C/ 


O 


I.  2. 


The  first  formula  shows  the  usual  benzene  ring  with  two  link- 
ing atoms  of  oxygen  replacing   two  hydrogen    atoms.     In  the 


QUINONES  351 

second,  two  carbonyl  groups  appear,  and  the  valence  require- 
ments are  met  by  the  omission  of  one  of  the  double  linkages, 
and  the  shifting  of  a  second  one. 

The  first  formula  explains  in  a  simple  manner  the  reduction 
OH  Cl 

/\  /\ 

to  quinol  ||       |,  and  the  formation  of  para-dichlorbenzene,  1 1       I, 

\/  \/ 

OH  Cl 

by  the  action  of  phosphorus  pentachloride;  while  the  second  form- 
ula requires  rearrangement  of  valencies  in  the  benzene  ring.  On 
the  other  hand  the  formulas  for  the  oximes, 

O  NOH 


and 


NOH  NOH 

are  derived  naturally  from  the  second  formula.  Further,  in  a 
chloroform  solution  of  quinone,  two  or  four  atoms  of  bromine 
may  be  added,  forming  C6H4Br2O2,  and  C6H4Br402.  This  is  a 
reaction  characteristic  of  an  unsaturated  compound,  and  is  ex- 
plained by  assuming  that  the  two  double  bonds  between  -carbon 
atoms  in  the  second  formula  are  like  the  double  bond  in  ethylene, 
and  are  easily  resolved  into  single  bonds: 
O 

O 
H  BrH/\HBr 

+   2Br2    =  | 

H\/H  BrH\/HBr 

O 
O 

These  and  other  considerations  have  led  to  the  adoption  of  the 
diketone  formula — the  second  one — for  the  quinones. 

Quinone  is  usually  prepared  by  oxidizing  aniline  with  potassium 
dichromate  and  sulphuric  acid,  and  extracting  with  ether.  It 


35 2  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

is  purified  by  distillation  with  steam.     The  golden-yellow  crystals 
melt  at  116°,  and  are  quite  soluble  in  hot  water. 

H/\H 

The  "quinoid  configuration,"      I        |      ,is   a    "  chromophore " 


group,  since  all  of  the  quinones  and  their  derivatives  are  colored 
compounds.  The  most  important  dyes  containing  this  group  are, 
however,  derivatives  of  aromatic  hydrocarbons  with  two  or  more 
"condensed"  benzene  rings,  such  as  naphthalene  and  anthracene, 
and  among  them  are  both  natural  and  artificial  dyes. 

Quinone  is  easily  converted  into  quinol  by  sulphurous  acid  and 
other  reducing  agents.  Hydrogen  chloride  and  hydrogen  bromide 
effect  a  peculiar  reaction,  changing  quinone  into  chlor  or  brom- 
quinol,  C6H3Br(OH)2.  The  steps  in  this  reaction  and  the  rear- 
rangements involved  are  probably, 


OH 

H 


OH 


Tetrachlorquinone  or  chloranil,  C6C14O2,  is  produced  by  the 
chlorination  of  quinone,  but  is  usually  prepared  by  the  simultane- 
ous oxidation  and  chlorination  (potassium  dichromate  or  chlorate 
and  hydrochloric  acid)  of  many  aromatic  substances.  It  is 
a  yellow  substance  which  melts  at  290°,  and  is  insoluble  in  water. 
It  is  readily  reduced  to  tetrachlorquinol,  C6Cl4(OH)2,  and  is  hence 
a  strong  oxidizing  agent,  and  employed  as  such  in  the  production 
of  certain  dyes. 


CHAPTER  XXVII 
AROMATIC  ACIDS 

The  carboxyl  group  which  is  characteristic  of  all  organic  acids 
cannot  be  developed  on  an  atom  of  nucleus  carbon,  and  hence, 
as  in  the  case  of  the  aldehydes,  the  aromatic  acids  are  compounds 
in  which  the  carboxyl  group  is  united  directly  or  by  linking  groups 
to  the  aryl  radical.  Of  these  two  classes  of  acids,  those 
with  directly  united  carboxyl  groups  are  much  the  more  important. 

Many  of  the  aromatic  acids  occur  in  nature  in  the  free  condition, 
or  as  esters, 'in  resins,  balsams,  and  essential  oils.  The  acids  are 
solid  crystalline  substances,  which  are  generally  somewhat  soluble 
in  hot  water,  but  almost  insoluble  at  ordinary  temperatures. 
Many  of  them  are  volatile  with  steam,  and  those  of  smaller 
molecular  weight  can  be  distilled  without  decomposition.  In 
solution  they  are  ionized  to  some  extent  and  usually  redden 
litmus.  They  decompose  carbonates,  and  are,  in  general, 
"stronger"  than  the  aliphatic  acids. 

Preparation. — i.  Both  classes  of  aromatic  acids  can  be  made 
by  the  methods  employed  for  the  formation  of  aliphatic  acids: 
oxidation  of  alcohols,  or  hydrolysis  of  nitriles  or  esters. 

2.  A  more  important  method  for  the  preparation  of  many  acids 
with  carboxyl  united  to  the  nucleus  is  by  oxidation  of  the  hydro- 
carbons with  side  chains.     All  side  chains  can  be  oxidized  to 
carboxyl   groups.     When   side   chains   of    different   lengths  are 
present  the  longer  is  usually  oxidized  first,  and  it  is  possible  to 
control  the  oxidation  so  that  one  or  more  carboxyl  groups  shall 
be  formed. 

3.  A  useful  method  is  by  the  oxidation  of  aryl-alkyl  ke tones 

23  353 


354  INTRODUCTION  TO   ORGANIC   CHEMISTRY 

(p.  348),  which  are  readily  formed  from  the  aromatic  hydrocar- 
bons and  acyl  chlorides  by  the  Friedel-Craf ts  reaction.  Thus  from 
mesitylene  and  acetyl  chloride,  acetomesitylene,  (CH3)3C6H2.CO.- 
CH3,  is  made,  and  then  oxidized  to  the  corresponding  acid, 
(CH3)3C6H2.CO.OH. 

4.  The  carboxyl  group  can  be  introduced  into  the  hydrocarbon 
in  place  of  hydrogen  by  the  action  of  carbonyl  chloride  in  the 
presence  of  aluminium  chloride  (Friedel-Crafts)  and  hydrolysis 
of  the  resulting  chloride;  or,  with  better  results,  by  carbonyl 
chloramide  (p.  233),  followed  by  hydrolysis: 

AlCli 

CHs.CeHs  +  C1.CO.NH2  ->  CH3C6H4.CO.NH2  +  HC1 

5.  The  aromatic  acids  can  also  be  prepared  by  the  Grignard 
reaction  (p.  37).     The  immediate  product  of  the  reaction,  e.g., 
CeH5.MgBr,   absorbs    carbon  dioxide  giving  CeH6.CO.OMgBr, 
and  this  on  treatment  with  hydrochloric  acid  yields  the  aromatic 
acid,  C6H5.CO.OH,  and  MgBrCl.     The  yield  is  nearly  that  in- 
dicated by  the  equation. 

6.  Halogen  can  be  replaced  by  carboxyl  by  the  action  of  carbon 
dioxide  in  the  presence  of  sodium: 

C6H5Br  +  CO2  +  2Na  =  C6H5.CO.ONa  +  NaBr 

Acids  which  have  the  carboxyl  group  in  a  side  chain  may  be 
prepared  by  the  acetoacetic  ester  synthesis  (p.  174). 

Reactions. — Salts  are  of  course  formed  by  the  action  of  the 
acids  on  hydroxides  or  carbonates.  The  alkali  salts  are  readily 
soluble  in  water,  and  the  acids  are  precipitated  from  them  by 
inorganic  acids.  The  silver  salts  are  frequently  employed  in 
determining  the  molecular  weight  of  the  acid,  since  on  ignition 
the  silver  is  left  in  a  pure  state. 

The  formation  of  esters,  acid  chlorides,  amides  and  anilides, 
and  the  replacement  of  the  carboxyl  group  by  hydrogen,  are 
accomplished  by  reactions  similar  to  those  employed  with  the 
aliphatic  acids  (p.  99). 


AROMATIC  ACIDS  355 

Chlorine  or  bromine,  or  the  sulphonic  acid  or  nitro  group  can  be 
introduced  into  the  aryl  radical  of  acids  directly,  and  these  nega- 
tive substituents  enter  chiefly  the  meta  position  with  reference 
to  the  carboxyl  group.  Other  derivatives  may  be  made  by  the 
usual  methods. 

An  unusual  reaction  is  that  which  produces  hydrogen  addition 
products  of  the  acids.  In  alkaline  solution  into  which  carbon 
dioxide  is  led,  sodium  amalgam  converts  benzoic  acid  into  tetra- 
hydrobenzoic  acid,  CeHg.CO.OH,  and  in  boiling  amyl  alcohol, 
benzoic  acid  is  reduced  to  hexahydrobenzoic  acid,  CeHn.CO.OH. 
Such  additions  of  hydrogen  take  place  more  easily  as  the  number 
of  carboxyl  groups  is  larger.  These  hydroaromatic  compounds 
are  discussed  in  Chapter  XXVIII. 

Benzoic  acid,  CeHs.CO.OH  (phenylformic  acid),  has  been 
known  since  the  beginning  of  the  seventeenth  century,  having 
been  originally  obtained  as  a  sublimate  from  gum  benzoin.  It 
is  present  in  gum  benzoin  chiefly  in  the  form  of  esters,  and  is 
also  found  in  other  plant  products,  such  as  balsams  of  Peru 
and  Tolu,  and  in  cranberries.  A  derivative  of  benzoic  acid,  the 
hippuric  acid  (p.  359),  is  present  in  the  urine  of  herbivora. 

While  it  may  be  made  by  any  of  the  methods  which  have  been 
given,  it  is  usually  prepared  for  pharmaceutical  purposes  by 
sublimation  from  gum  benzoin;  and  manufactured  on  a  large 
scale  from  toluene  by  converting  this  hydrocarbon  into  benzyl 
chloride,  C6H6.CH2C1,  and  then  oxidizing  the  latter  with  nitric 
acid.  The  direct  oxidation  of  toluene  gives  the  acid,  but  in  such 
small  amounts  that  its  preparation  through  the  chlorine  deriva- 
tive is  more  advantageous. 

Benzoic  acid  is  also  made  from  benzotrichloride,  CeHs.CCla, 
which  is  a  by-product  in  the  production  of  benzaldehyde,  by 
heating  this  with  milk  of  lime: 

3Ca(OH)2  =  2C6H5.CO.OH  +  3CaCl2  +  2H2O 


Benzoic  acid  is  nearly  odorless  when  perfectly  pure,  but  that 


356 


INTRODUCTION   TO    ORGANIC   CHEMISTRY 


made  from  gum  benzoin  has  a  slight  odor  of  the  aromatic  gum. 
It  sublimes  readily  and  its  vapors  are  very  irritating  to  the  nose 
and  throat.  Benzoic  acid  is  used  in  medicine,  in  the  preparation 
of  dyes,  aniline  blue  and  anthragallol.  The  latter  is  an  anthracene 
derivative  formed  from  benzoic  and  gallic  acids  by  elimination 
of  water: 


H                              OH  H     CO  OH 

H/\CO.OH          H/\OH  HX\/\/\OH 

HO.OC\/OH  HX/\/\/OH 

H                             H  H     CO  H 

Benzoic  acid                            Gallic  acid  Anthragallol 


o 

H\/] 


Sodium  benzoate  is  well  known  as  a  food  preservative. 


2H20 


Name 
Benzoic 

o-Toluic 
m-Toluic 
p-Toluic 

Cuminic 

Phenylacetic 

Cinnamic 

o-Phthalic 

m-(Iso)Phthalic 

p-(Tere)Phthalic 

Trimellitic 

Pyromellitic 

B  enzenepentacarboxy  lie 

Mellitic 


AROMATIC  ACIDS 

Formula    . 
C6H5.CO.OH 


3  (i) 

CO.OH  (2) 

I.  d) 

).OH  (3) 


/CH3        (i) 
CeH4\CO.OH  (4) 


C6H4< 


CH(CH3)2  (i) 
.CO.OH       (4) 


C6H6.CH2.CO.OH 
C6H5.CH:CH.CO.OH 
C6H4(CO.OH)2  (i,  2) 
C6H4(CO.OH)2  (i,  3) 
C6H4(CO.OH)2  (i,  4) 
C6H3(CO.OH)3  (i,  2,  4) 
C6H2(CO.OH)4  (i,  2,  4, 
C6H(CO.OH)6 
C6(CO.OH)6 


Melting  point 
121.4° 

104° 
109° 
180° 

116° 

76° 
133° 
231 

330°+ 
sublimes 
228° 
265° 

287° 


AROMATIC   ACIDS  357 

Toluic  acids,  CHs.CeH^.CO.OH.  The  three  isomeric  acids 
of  this  formula  can  be  made  by  partial  oxidation  of  the  three 
xylenes  with  nitric  acid,  or  from  the  toluidines  by  conversion  into 
nitriles  by  the  diazo  reaction  and  subsequent  hydrolysis.  Para- 
toluic  acid  is  also  readily  prepared  from  cymene  CH3.C6H4.C3H7, 
by  oxidation  of  the  isopropyl  group.  These  acids  present  no 
especial  points  of  interest,  nor  is  it  necessary  to  discuss  further 
the  homologues  of  benzoic  acid. 

Phenylacetic  acid,  C6H5.CH2.CO.OH,  which  is  isomeric  with 
the  toluic  acids,  is  best  obtained  by  the  hydrolysis  of  benzylcyan- 
ide,  C6H5.CH2.CN,  its  nitrile,  which  is  made  by  the  reaction 
of  benzylchloride,  CeHs-CH^Cl,  with  potassium  cyanide.  It  is 
a  slightly  weaker  acid  (less  ionized)  than  benzoic  acid,  though 
stronger  than  acetic  acid;  and  illustrates  the  general  fact  that 
with  wider  separation  of  the  phenyl  and  carboxyl  groups  by  in- 
termediate hydro-carbon  groups  the  acids  become  weaker. 

Phenylacetic  acid  can  yield,  of  course,  two  classes  of  derivatives, 
according  as  substitution  takes  place  in  the  nucleus  or  in  the  side 
chain.  On  oxidation  it  gives  benzoic  acid,  while  the  toluic  acids 
give  dibasic  phthalic  acids. 

Cinnamic  acid,  CeHs.CHiCH.CO.OH,  /3-phenylacrylic  acid, 
is  a  type  of  the  unsaturated  aromatic  acids  and  the  most  important 
of  the  group.  It  occurs  free,  and  in  esters  of  various  aromatic 
alcohols,  in  many  gums  and  balsams,  and  in  the  leaves  of  certain 
plants.  It  has  been  known  for  a  long  time,  and  was  formerly 
confused  with  benzoic  acid. 

It  is  prepared  from  storax,  or  is  synthesized  by  Perkin's 
reaction.  This  reaction,  which  is  the  most  important  method 
for  making  many  unsaturated  aromatic  acids  (and  also  applicable 
to  the  formation  of  unsaturated  aliphatic  acids),  consists  in  the 
condensation  of  an  aromatic  aldehyde  and  a  salt  of  an  aliphatic 
acid,  which  occurs  in  the  presence  of  acetic  anhydride: 

C6H5.CHO  +  CHa.CO.ONa  =  C6H5.CH:CH.CO.ONa+  H20 


INTRODUCTION   TO   ORGANIC   CHEMISTRY 

(Benzalchloride  may  be  used  here  in  place  of  benzaldehyde.) 

When  slowly  distilled,  or  more  readily  when  heated  with  lime, 
cinnamic  acid  gives  styrene,  C6H5.CH:CH2,  and  carbon  dioxide 
(calcium  carbonate). 

When  cinnamic  acid  is  oxidized,  the  double  bond  becomes  the 
point  of  attack;  a  mild  oxidation  (KMnO4)  yielding  phenyl- 
glyceric  acid,  C6H6.CHOH.CHOH.COOH,  and  a  stronger  oxida- 
tion (HNOs)  giving  benzaldehyde  and  benzoic  acid. 

As  an  unsaturated  compound  it  unites  with  halogens  to  form 
dihalogen  derivatives,  e.g.,  Ce^.CHCl.CHQ.CO.OH;  and  by 
reduction  with  sodium  amalgam  it  gives  hydro  cinnamic  acid,  or 
phenylpropionic  acid,  CeH5.CH2.CH2.CO. OH. 

By  the  usual  reactions  for  producing  unsaturation  (p.  45) 
cinnamic  acid  may  be  converted  into  phenylpropiolic  acid,  CeHs- 
C  =  C.CO.OH,  and  from  this,  phenylacetylene,  C6H5.C  ='CH, 
can  be  prepared  (p.  279). 

Derivatives  of  the  Monobasic  Acids 

Benzoyl  Chloride,  CeHs.CO.Cl,  is  formed  like  other  acyl  chlo- 
rides by  the  action  of  phosphorus  pentachloride  on  benzoic  acid 
or  its  sodium  salt;  but  it  is  usually  prepared  in  quantity  by  treat- 
ing benzaldehyde  with  chlorine  (p.  346),  a  reaction  that  differs 
from  that  of  chlorine  with  aliphatic  aldehydes  (cf.  p.  80). 

Benzoyl  chloride  is  a  liquid  of  disagreeable,  tear-compelling  odor 
that  boils  at  198°.  It  is  insoluble  in  water  but  is  slowly  decom- 
posed by  it  with  the  formation  of  benzoic  and  hydrochloric  acids 
(cf.  p.  115).  It  reacts  with  practically  all  alcohols  and  phenols, 
primary  or  secondary  amines,  with  the  formation  of  benzoyl  com- 
pounds which  are  useful  in  the  identification  and  characteriza- 
tion of  these  substances.  These  reactions  are  greatly  facilitated 
by  the  presence  of  an  alkali  (Schotten-Baumann  reaction)  : 
C6H5.CO.C1  +  C2H5OH  +  NaOH  =  C6H5CO.OC2H5  +  NaCl 

+  H20 

C6H5.CO.C1  +  C6H5NH2  +  NaOH   =   C6H5.CO.NHC6H5  + 

NaCl  +  H20 


AROMATIC   ACIDS  359 

Benzamide,  C6H5.CO.NH2,  is  readily  prepared  by  bringing 
together  benzoyl  chloride  and  ammonia  or  ammonium  carbonate. 
It  crystallizes  from  hot  water  in  glistening  plates  that  melt  at 
128°.  One  hydrogen  atom  of  the  amido  group  is  replaceable  by 
metals  (cf.  p.  140),  and  the  metal  may  in  turn  be  replaced  by 
alkyl  radicals  by  the  action  of  alkyl  halides.  Like  the  aliphatic 
amides  benzamide  appears  to  exist  in  two  forms  (cf.  p.  141). 

Benzonitrile,  C6H5.CN,  can  be  formed  by  the  withdrawal  of 
water  from  benzamide,  (P2O5),  but  is  best  prepared  from  anilin 
by  the  Sandmeyer  reaction  (p.  316).  It  is  a  liquid  with  the  odor 
of  bitter  almonds  and  boils  at  191°.  It  has  all  the  properties  of 
the  aliphatic  nitriles  (p.  153). 

Hippuric  Acid,  C6H5.CO.NH.CH2.CO.OH,  which  occurs  in 
the  urine  of  herbivora,  is  benzoylglycine,  and  can  be  made  by  shak- 
ing a  mixture  of  benzoylchloride  and  aminoacetic  acid  (glycine) 
with  sodium  hydroxide: 

C6H5.CO.C1  +  NH2CH2.CO.OH  = 

Benzoyl  chloride  Glycine 

C6H5.CO.NH.CH2.CO.OH  +  HC1 

Hippuric  acid 

Benzoic  acid  was  formerly  obtained  to  some  extent  from  the 
natural  hippuric  acid,  which  was  discovered  in  1776  in  the 
urine  of  cows  and  camels.  Hippuric  and  benzoic  acids  were 
not  clearly  distinguished  until  1829  (Liebig). 

/co\ 

Saccharin,    CeH4<^        y>NH  (i,  2),  is  o-sulphobenzoic-acid- 

imide  and  a  derivative  of  the  ortho  sulphonic  acid  of  benzoic  acid. 
Since  the  chief  product  of  the  sulphonation  of  benzoic  acid  is  the 
meta  compound,  the  starting  point  for  the  preparation  of  sac- 
charin is  toluene.  The  steps  are: 


C6H5.CH3-»C6H4  -^C6 

XSO3  OH  S02C1  S02NH2 

Toluene  Toluene  sulphonic       Toluene  sul-          Toluene  sulphonamide 

acid  phonyl  chloride 


360  INTRODUCTION   TO   ORGANIC   CHEMISTRY 


/CO.OH  /COv 

C6H4<  -»  C6H/        >NH 

XS02NH2  XSO/ 

Toluic  acid  Saccharin 


In  the  sulphonation  of  toluene,  both  ortho  and  para  sulphonic 
acids  are  produced.  These  are  converted  into  the  acid  chlorides, 
and  as  the  para  chloride  is  a  solid  and  the  ortho  a  liquid,  they  may 
be  largely  separated.  The  ortho  compound  is  then  converted 
into  the  amide  by  ammonia  and  the  amide  oxidized  by  potassium 
permanganate  in  neutral  solution.  On  adding  hydrochloric 
acid  to  the  solution,  saccharin  is  obtained.  It  was  discovered  in 
1879  by  Fahlberg  and  Remsen. 

It  is  a  colorless,  crystalline  substance,  which  melts  with  some 
decomposition  at  224°.  It  is  only  slightly  soluble  in  water. 
Its  most  striking  property  is  its  intensely  sweet  taste,  which  is 
said  to  be  more  than  500  times  that  of  cane  sugar.  On  this 
account  it  is  manufactured  and  used  for  sweetening  purposes, 
and  as  a  substitute  for  sugar  by  sufferers  from  diabetes. 

yCO.OH     (l) 

Anthranilic  Acid,  C6H4<(  ,   o-aminobenzoic  acid,  is 

\NH,        (2) 

of  especial  interest  on  account  of  its  relation  to  indigo  and  its 
use  in  the  artificial  preparation  of  this  dye.  It  was  first  obtained 
from  indigo  (anil)  by  boiling  this  substance  with  potassium 
hydroxide. 

The  three  aminobenzoic  acids  can  be  made  by  reduction  of  the 
corresponding  nitro  compounds;  but  the  o-nitrobenzoic  acid  is  a 
minor  product  of  direct  nitration  of  benzoic  acid.  Anthranilic 
acid  is  prepared  for  making  indigo  from  naphthalene  by  the 
series  of  reactions  shown  by  the  following  formulas: 

o  /CO.OH  /C 

4H4  ->  C6H4<  ->  C6H4< 

XCO.OH 

Naphthalene  o-Phthalic  Phthalic 

acid  anhydride 


AROMATIC   ACIDS  361 

/CONH2  /NH2 

C6H4<  ->  C6H/ 

XCO.OH  XCO.OH 

Phthalic  o-Aminobenzenoic 

amide  acid 

The  last  reaction  is  accomplished  by  bleaching  powder  and  is 
Hofmann's  reaction  for  the  formation  of  amines,  (cf.  p.  129). 

Anthranilic  acid  melts  at  145°  and  decomposes,  on  distillation, 
into  aniline  and  carbon  dioxide.  By  reaction  with  chloracetic 
acid,  and  fusion  of  the  product  with  sodium  hydroxide,  indoxyl 
is  produced,  which  in  dilute  solution  is  oxidized  to  indigo  by  the 
air  (p.  400). 

Hydroxy  Acids 

Hydroxy  or  phenol  acids  can  be  made  by  the  introduction  of 
hydroxyl  groups  into  acids:  i.  through  nitro  derivatives  by 
reduction  of  the  nitro  to  the  amino  groups  followed  by  the  diazo 

reaction : 

/CO.OH  /CO.OH 

C6H5.CO.OH  ->  C6H4<  -» C6H4<  -> 

XNH2 


/CO.OH  /CO.OH 

CTT   /  f*    TT    / 

6-tl4\  ~*  L^6-tl-4\ 

XN2C1  XOH 

2.  or  through  the  sulphonic  acids  by  fusion  with  potassium 
hydroxide: 

/CO.OH  KOH          /CO.OH 

C6H6.CO.OH  ->  C6H4<  >  C6H< 

\gQ3jj  ^OH 

3.  The  carboxyl  group  can  be  introduced  into  phenols  by  way 
of  the  nitro  derivatives.  The  nitro  group  is  reduced  to  the  amino 
group,  the  cyanogen  group  is  substituted  for  this  by  Sandmeyer's 
reaction  (p.  316),  and  the  resulting  nitrile  is  finally  converted  into 
the  carboxyl  group  by  hydrolysis : 


362  INTRODUCTION   TO    ORGANIC   CHEMISTRY 


OH 


C6H4 


/OH  /OH 

/  v    rvti./ 


-        64 
X  X 


NO2  NH2  N2C1 


/OH  /O 

C6H4<          ->    C6H< 
XCN  XC 


H 
CO.OH 

4.  Homologues  of  phenol  are  converted  into  phenol  acids  by 
the  oxidation  of  the  side  chains.     The  reaction  is  particularly 
successful  when  the  phenols  are  first  changed  into  their  sulphuric 
acid  or  phosphoric  acid  esters. 

5.  An  important  method  for  making  hydroxy  acids  is  by 
Kolbe's  synthesis.     As  originally  carried  out,  an  alkali  phenolate 
is  heated  in  a  current  of  carbon  dioxide  with  the  result  that  half 
distils  as  phenol,  and  the  rest  is  converted  into  the  basic  salt  of  the 
hydroxy  acid: 


2C6H6ONa  +  CO2  =  C6H6OH  +  C6H4< 

xCO.ONa 

But  if  the  alkali  phenolate  is  heated  with  carbon  dioxide  under 
pressure,  it  is  completely  transformed  into  the  normal  salt  by 
intramolecular  change,  a  phenylcarbonate  being  formed  as  an 
intermediate  step : 

/OH 
C6H5ONa  +  CO2  =  C6H5OCO.ONa  =  C6H4< 

XCO.ONa 


It  is  an  interesting  fact  that  the  ortho  compound  results  when 
sodium  phenolate  is  used,  while  potassium  phenolate  at  tempera- 
tures from  170°  to  210°  yields  the  salt  of  the  para  hydroxy  acid. 
The  formation  of  the  meta  compound  by  this  method  has  not  been 
observed. 

Properties. — The  hydroxy  acids  are  colorless,  crystalline  sub- 
stances, more  soluble  in  water  (influence  of  hydroxyl  groups)  than 
the  acids  from  which  they  are  derived.  The  hydrogen  of  the 


AROMATIC  ACIDS  363 

hydroxyl,  as  well  as  that  of  the  carboxyl,  is  replaced  by  an  alkali 
metal  when  the  hydroxy  acid  is  treated  with  an  alkali  hydroxide, 
but  these  salts  are  changed  to  mono-metal  salts  of  the  hydroxy 
acids  by  carbon  dioxide;  and  by  alkali  carbonates  only  the  hydro- 
gen of  the  carboxyl  group  is  replaced.  They  are  converted  into 
phenols  by  heating  with  lime, — the  general  reaction  for  replac- 
ing the  carboxyl  group  with  hydrogen: 

C6H4(OH).CO.OH  +  CaO  =  C6H5OH  +  CaCO3 

Effect  of  Position.  The  relative  positions  of  the  carboxyl  and 
the  hydroxyl  groups  have  a  striking  influence  on  their  activity 
as  acids,  as  shown  by  the  ionization  constants  (see  also  p.  408). 

kxio* 

Benzoic  acid 6.6 

o-Hydroxybenzoic  acid 100 . 

m-Hydroxybenzoic  acid 8.3 

p-Hydroxybenzoic  acid 2.8 

2,  6-Dihydroxybenzoic  acid 5000 . 

It  is  seen  from  these  figures  that  the  hydroxyl  group  in  the 
meta  position  produces  little  effect,  and  in  the  para  position 
decreases  the  acidity  to  less  than  one-half  that  of  the  simple 
acid.  In  the  ortho  position,  however,  the  acidity  is  very  greatly 
increased, — 17  times  by  a  single  hydroxyl  group,  and  833  times 
when  two  stand  in  the  ortho  position  to  the  carboxyl  group. 
Similar  influences  are  found  in  the  case  of  other  substitutes,  and 
are  most  marked,  as  here,  when  they  occupy  the  ortho  position. 
Thus  the  constant  for  o-nitrobenzoic  acid  is  100  times  that  of 
benzoic  acid,  that  for  o-brombenzoic  acid  is  24  times,  and  that 
for  o-methyl-benzoic  acid  (o-toluic)  2  times  as  large. 

The  ortho  hydroxy  acids  differ  from  the  meta  and  para  com- 
pounds also,  in  that  they  alone  give  the  violet  coloration  with 
ferric  chloride  which  is  characteristic  of  phenol,  and  are  volatile 
with  steam.  Ortho  and  para  hydroxy-acids  are  much  more  read- 
ily converted  into  phenols  by  heating  alone  or  with  concentrated 


364  INTRODUCTION   TO    ORGANIC   CHEMISTRY 

hydrochloric  acid  than  are  the  meta  compounds,  and  the  greater 
stability  of  the  latter  is  indicated  by  other  reactions. 

HYDROXY-ACIDS 

Name  Formula  Melting  point 

Mandelic  C6H6.CH.OH.CO.OH  118° 

Phenyl-lactic  C6H6.CH2.CH.OH.CO.OH  98° 

Salicylic  acid  C6H4<£°'°H  £>  159° 


C, 

Protocatechuic 


T  /CO.OH  (i) 
Galhc  C6H<(OH)3(3,4,5) 

Mandelic  acid,  CeHe.CH.OH.CO.OH,  phenylglycollic  acid, 
is  the  simplest  hydroxy-acid  which  has  hydroxyl  in  a  side  chain. 
It  was  originally  obtained.from  bitter  almonds  (German,  Bitter- 
mandel).  The  amygdalin  contained  in  the  almonds  breaks  up, 
as  we  have  seen,  into  benzaldehyde,  hydrocyanic  acid  and  glucose 
(p.  345).  The  mandelic  acid  is  the  result  of  the  union  of  the  alde- 

, 
hyde  and  acid,  forming  the  cyanhydrin,  CeH5.CH<f 

XCN 

followed  by  the  hydrolysis  of  this  substance,  which  is  the  nitrile  of 
mandelic  acid.  It  is  usually  prepared  by  this  reaction,  but  start- 
ing with  benzaldehyde  already  made.  From  the  synthetic  man- 
delic acid  which  is  optically  inactive,  like  all  synthetic  products, 
dextro  and  levo  rotatory  acids  can  be  obtained  by  the  methods 
employed  in  the  case  of  other  active  compounds  (p.  192). 

Mandelic  acid  resembles  lactic  acid  —  methylglycottic  acid  —  in 
many  respects,  as  might  be  expected  from  a  comparison  of  their 
formulas. 


AROMATIC  ACIDS  365 

/OH  (l) 

Salicylic  acid,  CeH^  ,   o-oxybenzoic    acid,   is    the 

XCO.OH  (2) 

only  important  mono-hydroxybenzoic  acid  It  occurs  free  in  the 
buds  of  spircza  ulmaria,  and  in  some  other  plants;  and  as  methyl 
ester  in  oil  of  wintergreen  and  other  ethereal  oils.  It  was  first 
obtained  (1838)  from  salicylic  aldehyde  (p.  346)  and  was  named 
from  this.  It  was  formerly  prepared  from  oil  of  wintergreen, 
but  is  now  made  commercially  from  phenol  by  Kolbe's  method 
(p.  362).  It  melts  at  159°  and  on  careful  heating,  sublimes  with- 
out decomposition,  but  on  sharp  heating,  partially  decomposes 
into  phenol  and  carbon  dioxide.  Heated  for  some  time  at  200°- 

OH 
220°,  it  is  largely  converted  into  Salol,  CeH^  its 

XCO.OC6H6 

phenyl  ester,  a  substance  much  used  in  medicine  on  account  of 
its  antiseptic  properties.  Salicylic  acid  itself  is  a  powerful  anti- 
septic, and  as  it  has  no  odor,  is  often  used  in  place  of  phenol  as  a 
disinfectant.  It  is  also  used  as  a  preservative  for  foods,  etc., 
and  its  salts  and  certain  derivatives  are  employed  in  medicine. 
especially  acetyl  salicylic  acid,  known  as  "aspirin," 

,O.OC.CH3 


XCO.OH 

/co.on  (i) 

Anisic  acid,  CeH^  ,  p-methoxybenzoic  acid,  is  ob- 

X)CH,     (4) 

tained  by  oxidizing  anethol  (p-propenyl  anisol)  (p.  347),  which 
is  the  chief  constituent  of  anise  oil.  It  has  long  been  known,  is 
readily  obtained,  and  it  and  its  derivatives  have  been  much 
studied. 

yCOOH   (l) 

Protocatechuic  acid,  C6H3  ^  ,  dioxybenzoic  acid,  is 

3,  4) 


366  INTRODUCTION   TO    ORGANIC    CHEMISTRY 

the  most  important  of  the  six  possible  isomeric  dihydroxy  acids. 
It  is  obtained  from  many  resins  and  some  tannins,  and  other  sub- 
stances by  fusion  with  potassium  hydroxide.  Protocatechuic 
acid  belongs  to  a  class  of  compounds  which  may  be  regarded  as 
derivatives  of  catechol  (p.  333)  in  which  a  third  group  stands  in  a 
position  para  to  one  hydroxyl,  and  meta  to  the  other.  Com- 
pounds with  this  grouping  are  found  frequently  in  nature,  as  for 
instance,  eugenol,  safrol,  and  vanillin. 

Protocatechuic  acid  solutions  are  colored  bluish-green  by  ferric 
chloride,  and  the  color  changes  to  blue  and  finally  to  red  on  addi- 
tion of  dilute  alkalies.  It  reduces  ammoniacal  silver  nitrate,  but 
does  not  reduce  Fehling's  solution. 

The  m-methyl  ether  of  protocatechuic  acid  is  vanillic  acid, 

/COOH  (i) 
CeHg^-OCHa    (3),  and  can  be  obtained  by  oxidation  of  vanillin 

\OH       (4) 

(p.  347)  which  is  the  corresponding  aldehyde,  and  from  other 
substances.     The  dimethyl  ether  is  veratric  acid,  and  the  methylene 

/CO.  OH 
ether,  CeHa—  0—  CH2,  is   piperonylic  acid,  both  of   which  are 


obtained  from  vegetable  substances. 

yCO.OH  (l) 

Gallic  acid,  CeH^  ,  is  the  only  one  of  the  tri- 

^(OH)3  (3,  4,  5) 

hydroxybenzoic  acids  which  needs  to  be  described.  There  are 
six  possible  acids  of  this  formula,  and  three  of  them  are  known. 
Gallic  acid  occurs  free  in  gall-nuts,  tea,  and  in  the  astringent 
parts  of  the  sumach  and  many  other  plants.  It  is  readily  ob- 
tained from  tannins  by  boiling  them  with  dilute  acids,  or  by  the 
action  of  moulds  on  their  solutions.  It  crystallizes  with  one 
molecule  of  water  in  glistening  needles,  and  loses  its  water  at  120°. 
It  has  no  definite  melting  point,  decomposing  at  temperatures 
above  220°  into  pyrogallol  (p.  335)  and  carbon  dioxide.  With 


AROMATIC   ACIDS  367 

ferric  chloride  its  solutions  give,  according  to  the  concentration, 
a  bluish  or  greenish  black  color  (or  precipitate),  and  it  reduces 
Fehling's  solution  and  solutions  of  silver  and  gold  salts. 

It  is  employed  in  the  preparation  of  pyrogallol,  as  a  photo- 
graphic developer,  and  in  making  certain  dyes,  such  as  "gallo- 
flavin"  (by  oxidation  of  its  alkaline  solutions  in  air),  and  of 
"anthracene  brown." 

Tannic  acids  or  tannins,  are  amorphous  substances  which  occur 
widely  distributed  in  the  vegetable  kingdom.  The  principal 
commercial  sources  are  the  bark  of  the  oak  and  hemlock,  sumach, 
gall-nuts,  and  a  number  of  Indian  and  South  American  trees. 
Tannin  is  used  for  tanning  leather,  as  a  mordant  in  dyeing,  in 
ink-making,  and  as  the  source  of  gallic  acid  and  pyrogallol. 

Some  tannins  yield  gallic  acid  and  glucose  on  hydrolysis  and 
thus  appear  to  be  glucosides.  These  tannins  give  a  blue  black 
color  with  ferric  chloride.  Others  are  colored  green  by  ferric 
chloride  and  give  catechol  when  heated. 

All  tannins  are  astringent  in  taste,  soluble  in  water  and  alcohol, 
and  do  not  melt  without  decomposition.  A  characteristic 
property  is  that  of  forming  insoluble  compounds  with  gelatin  or 
gelatin-forming  tissues,  and  on  this  their  use  in  leather-making 
depends. 

Iron  inks  are  usually  made  from  ferrous  sulphate  and  the  tannin 
obtained  from  gall-nuts.  In  the  older  iron  inks  the  nearly  color- 
less solution  was  oxidized  by  the  air  with  the  formation  of  a  finely 
divided  and  nearly  black  precipitate,  which  was  held  in  suspension 
by  the  addition  of  gum.  In  the  more  modern  iron  inks  the  oxi- 
dation is  prevented  by  the  addition  of  acid,  and  the  almost  color- 
less solution  is  temporarily  colored  for  writing,  with  a  coal  tar  dye. 
The  black  color  of  the  ink  proper  develops  on  the  paper  through 
atmospheric  oxidation.  Many  inks  are  made  of  other  materials 
and  very  commonly  consist  of  solutions  of  coal  tar  dyes. 

Gallotannic  acid  or  digallic  acid,  occurs  as  a  glucoside  in  gall- 
nuts,  forming  about  70  per  cent,  of  their  weight.  It  is  extracted 


368  INTRODUCTION   TO   ORGANIC   CHEMISTRY 

by  ether  and  alcohol.  Its  empirical  formula  is  CuHioOg,  and  its 
structure,  as  inferred  from  its  synthetical  formation  from  gallic 
acid  by  heating  with  phosphorus  oxychloride  is: 


HO/NcO  -  O/\CO.OH 


OH  HO 

It  is  resolved  into  gallic  acid  by  hydrolysis. 

Polycarboxylic  Acids 

Aromatic  acids  with  two,  three,  four,  five,  and  six  carboxyl 
groups  are  all  known.  Of  these  only  those  with  two  and  six 
carboxyl  groups  are  of  particular  interest. 

Phthalic  acids,  C6H4(CO.OH)2.  Acids  of  this  formula  are  the 
oxidation  products  of  all  benzene  homologues  with  two  side  chains, 
and  hence  have  been  used  as  reference  compounds  in  determin- 
ating the  position  of  the  side  chains.  Their  name  is  derived  from 
naphthalene  from  which  the  first  one — the  ortho  acid — was 
obtained. 

Orthophthalic  acid,  usually  called  simply  phthalic  acid,  is  the 
most  important  of  the  three  isomers,  being  extensively  manufac- 
tured for  the  preparation  of  phthalein  dyes,  and  of  anthranilic 
acid  which  serves  as  a  step  in  making  artificial  indigo. 

Its  technical  production  is  from  naphthalene  by  oxidation  with 
concentrated  sulphuric  acid  and  mercury  sulphate  at  a  temperature 
above  300°.  o-Phthalic  acid  differs  from  its  two  isomers  by  its 
much  greater  solubility,  and  by  the  facts  that  it  has  no  definite 
melting  point,  and  gives,  on  heating,  a  crystalline  sublimate  of 
its  anhydride.  The  meta  acid — isophthalic  acid — and  the  para  acid 
— terephthalic  acid — both  sublime  unchanged,  the  latter  without 
melting.  Another  characteristic  difference  is  shown  by  o-phthalic 
acid  in  the  fluorescein  reaction  which  its  anhydride  gives  with 
resorcinol  (p.  334).  By  chromic  acid  it  is  easily  and  completely 


AROMATIC   ACIDS  369 

oxidized;  on  heating  with  lime  to  33o°-35o°,  it  yields  benzoic 
acid;  and  benzene  is  formed  when  it  is  distilled  with  lime. 


O, 


O,  sublimes  from  o-phthalic 

acid  in  beautiful  long  crystals.  It  melts  at  128°  and  boils  at 
284.5°.  When  heated  with  phenol  and  concentrated  sulphuric 
acid,  phthalic  anhydride  gives  phenolphthale'in.  This  is  only 
slightly  soluble  in  water,  but  dissolves  readily  in  alcohol.  Its 
neutral  or  acid  solutions  are  colorless,  but  in  alkaline  solutions  it 
becomes  intensely  red.  On  this  account  and  because  it  is  sensitive 
even  to  weak  acids,  it  is  much  employed  as  an  indicator  in  titrating 
acids  and  bases.  Its  constitution  appears  to  be: 

(4)  d)  (4) 

HOC6H4.  -  C  -  C6H4.OH 


C6H4      O 


CO  (2) 

In  alkaline  solution  it  is  converted  into  a  salt, 
NaOC6H4.C  =  C6H4  =  O 
I 

C6H4.CO.ONa 
in  which  by  molecular  rearrangement  a  quinoid  group, 

=  C6H4  = 

is  present  (cf.  p.  352): 

Fluoran  is  formed  as  a  by-product  in  making  phenolphthalein. 
Its  structure  is  thus  indicated, 


C6H4-C-C6H4O  C' 

/\  or  /I 

C6H4      O  C6H4  O 

V  M 

CO  CO 


It  is  insoluble  in  alkalies. 


370  INTRODUCTION   TO   ORGANIC    CHEMISTRY 

Fluoresceiin  is  a  dihydroxyl  derivative  of  fluoran,  formed  by 
heating  phthalic  anhydride  with  resorcinol.  Dilute  alkaline 
solutions  of  it  show  a  strong  yellow  green  fluorescence,  which  is 
so  intense  that  it  can  be  recognized  in  the  weakest  solutions.  A 
number  of  its  halogen  derivatives  are  useful  dyes.  Among  them 
is  eosin  which  is  an  alkali  salt  of  tetrabromfluorescein.  Its 
solutions  are  rose  colored  and  show  the  same  fluorescence  as 
fluorescem.  The  corresponding  iodine  compound,  iodeosin,  is 
used  as  an  indicator  for  acids  and  alkalies. 

CC12 


Phthalyl  Chloride  appears  from  its  reactions  to  be  CeH4       O 

CO 
xCO.Cl 

rather  than  the  normal  chloride  C6H4<^  .     It    is    an    oil 

^CO.Cl 

which   boils   at  276°.     Sodium  amalgam   and  water  change  it 
CH2 

to  phthalide,  C6H4        O  which  is  a  lactone  (p.  172). 

CO 

Mellitic  acid,  C6(CO.OH)6,  is  found  in  the  form  of  its  hydrated 
aluminium  salt  in  some  lignite  beds.  This  salt,  which  is  called 
honey  stone  from  its  color,  gives  the  name  to  the  acid  (met,  honey). 
The  acid  can  be  obtained  from  honeystone  or  made  by  oxidation 
of  hexamethylbenzene,  which  can  be  synthesized  from  benzene 
or  its  methyl  derivatives  with  methyl  halide  by  the  Friedel-Craft's 
reaction.  It  is  also  formed  by  the  oxidation  of  carbon,  in  the  form 
of  graphite,  by  alkaline  permanganate;  from  charcoal,  by  heating 
with  sulphuric  or  nitric  acid;  and  by  the  electrolytic  oxidation 
of  carbon  anodes. 

Mellitic  acid  is  readily  soluble  in  water  and  in  alcohol,  and 
crystallizes  from  solution  in  fine,  silky  crystals.  It  is  quite 
stable,  but  on  dry  distillation  yields  pyromellitic  anhydride, 


AROMATIC  ACIDS 


cox 

O,  and  like  all  acids  has  all  its  carboxyl  groups  re- 


o 


placed  by  hydrogen  when  distilled  with  lime.  Through  meilitic 
acid,  therefore,  the  benzene  ring  can  be  built  up  from  elementary 
carbon,  and  benzene  itself  obtained.  Meilitic  acid  is  readily 
converted  by  reducing  agents  in  ammoniacal  solution  into  hexa- 
hydromellitic  acid,  C6H6.(CO.OH)6. 


CHAPTER  XXVIII 

HYDROAROMATIC  HYDROCARBONS  AND  THEIR 
DERIVATIVES 

Terpenes  and  Camphors 

When  benzene  vapor  and  hydrogen  are  passed  over  finely 
divided  nickel  at  i8o°-2oo°,  hexahydrobenzene,  CeHi2,  is  obtained 
(Method  of  Sabatier  and  Sendersen).  On  treatment  with  bromine, 
this  compound  forms  a  substitution  product,  CeHnBr,  and  from 
this,  tetrahydrobenzene,  CeHio,  is  produced  by  digestion  with  alco- 
holic potassium  hydroxide: 

CeHnBr  +  KOH  =  C^o  +  KBr  +  H2O 


Tetrahydrobenzene  is  an  unsaturated  compound  and  combines 
additively  with  bromine,  yielding  C6Hi0Br2;  and  this  dibrom- 
hexahydrobenzene,  when  treated  with  alcoholic  potassium 
hydroxide  gives  dihydrobenzene,  C6H8. 

The  structural  relations  of  the  three  hydrobenzenes  to  benzene 
and  to  each  other  are  represented  by  the  following  formulas, 

H  H2  H 

C  C  C 

S\  /\  ^\ 

HC        CH  H2C        CH2  HC        CH2 

I         II  II  II 

HC        CH  H2C        CH2  H2C        CH2 

\/  V  \/ 

C  C  C 

H  H2  H2 

f-*\      1"|-  X~t      TT  /""*      TT 

Ue-tle  v^G-n-12  *— e-n-io 

Benzene  Hexahydrobenzene  Tetrahydrobenzene 

371 


INTRODUCTION   TO  ORGANIC    CHEMISTRY                372 

H  H 

C  C 

s\  /\ 

HC        CH2  H2C        CH 

II  II 

H2C        CH  H2C        CH 


c  c 

H  H 

CeHg  CeHa 

Dihydrobenzene 

As  in  the  case  of  quinone  (p.  350),  the  valence  requirements  in 
the  hydrobenzene  formulas  are  met  by  the  change  of  one  or  more 
of  the  double  linkages  of  the  benzene  ring  to  single  bonds.  Two 
formulas  for  dihydrobenzene  are  given,  representing  the  two  possi- 
ble relative  positions  of  the  two  double  bonds.  Two  correspond- 
ing hydrocarbons  are  known. 

It  should  be  noticed  that  while  hexahydrobenzene  behaves  as  a 
saturated  hydrocarbon,  giving  substitution  products  with  halo- 
gens, the  tetra  and  dihydrobenzenes  are  unsaturated,  absorbing 
two  and  four  atoms  of  chlorine  and  bromine  respectively,  and 
decolorizing  permanganate.  According  to  the  formulas  given 
above,  the  presence  of  one  or  two  double  linkages  gives  an  un- 
stable condition  as  in  the  olefines.  In  benzene,  which,  according 
to  the  Kekule  formula,  has  three  double  bonds,  the  condi- 
tion is  much  more  stable,  though  benzene  does  unite  with  chlorine 
in  sunlight  to  form  CeHeCle,  and  with  hydrogen  to  form  CeHi2, 
as  we  have  just  seen. 

Other  aromatic  hydrocarbons  are  also  hydrogenated  to  hexa- 
hydrobenzene derivatives  by  the  method  given  for  benzene;  and 
a  number  of  aromatic  derivatives  unite  with  hydrogen  through  the 
action  of  reducing  agents.  The  reduction  of  benzoic  acid  to 
hexahydrobenzoic  acid  has  been  already  given  (p.  355),  and  the 
reduction  of  polycarboxylic  acids  is  readily  effected  by  sodium 
amalgam  in  aqueous  solutions. 


373  HYDROAROMATIC   HYDROCARBONS 

While  the  hydroaromatic  compounds  are  thus  related  to  the 
aromatic  substances,  and  undoubtedly  contain  rings  of  six  carbon 
atoms,  they  are  also  related  to  aliphatic  compounds  in  their 
behavior,  and  by  the  fact  that  many  of  them  can  be  made  by 
synthesis  from  these  compounds.  From  this  point  of  view  they 
are  cycloparaffins — and  hexahydrobenzene  is  also  called  hexa- 
methylene  or  cyclohexane  (cf.  p.  258).  A  number  of  compounds 
belonging  to  this  group  occur  naturally,  and  some  of  them  are  of 
considerable  importance. 

Properties. — Hexahydrobenzene  and  the  homologous  hydro- 
carbons are  thin,  volatile  oils  having  an  odor  like  that  of  "  ben- 
zine." Toward  chemical  agents  they  act  more  like  saturated 
paraffins  than  like  aromatic  hydrocarbons.  Nitric  and  sulphuric 
acids  leave  them  unchanged  under  conditions  which  lead  to  the 
formation  of  nitro  and  sulphonic-acid  products  with  benzene  and 
its  homologues,  and  advantage  is  taken  of  this  indifference  in 
separating  the  hydroaromatic  from  the  aromatic  hydrocarbons. 
When  boiled  with  strong  nitric  acid,  however,  cyclohexane  is  con- 
verted chiefly  into  normal  adipic  acid,  CO.OH.(CH2)4.CO.OH, 
with  rupture  of  the  ring  configuration;  and  homologues  of  cyclo- 
hexane containing  methyl  groups  have  been  changed  into  nitro 
compounds  of  the  corresponding  aromatic  hydrocarbons  by  the 
simultaneous  oxidizing  and  nitrating  action  of  nitric  acid.  With 
bromine  in  the  presence  of  aluminium  bromide,  aromatic  deriva- 
tives have  been  obtained,  e.g.,  tetrabromxylene,  C6Br4(CH3)2, 
from  dimethylcylohexane,  CeHioCCHs^.  Chlorine  substitution 
products  are  formed  more  readily  than  with  the  aromatic 
hydrocarbons. 

Cyclohexane  and  methylcyclohexane  are  found  in  Russian 
petroleum.  Cyclohexane  has  almost  the  same  boiling  point  as 
benzene  (80. 2°) .  Both  of  the  unsaturated  hydrocarbons,  dihydro- 
and  tetrahydrobenzene,  have  been  found  in  coal  tar. 

Of  the  hydroxyl  derivatives  of  cyclohexane,  quercite,  CeHy- 
(OH)5  (quercus,  oak)  is  found  in  acorns,  and  inosite,  (C6H6(OH)6 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  374 

"s,  <Ws,  muscle,  is  widely  distributed  in  many  leguminous  plants), 
and  in  animal  tissues.  Both  of  these  substances  have  a  sweet 
taste  and  were  formerly  classed  with  the  sugars.  It  will  be  noted 
that  inosite  has  the  same  molecular  formula  as  the  hexoses. 

Quercite  is  dextro-rotatory;  inosite  is  optically  inactive  and 
cannot  be  resolved  into  active  components.  Methyl  ethers  of 
dextro  and  levo  inosite  are,  however,  found  in  certain  plants, 
and  from  them  the  optically  active  inosites  can  be  prepared.1 

The  constitution  of  these  substances  is  shown  by  their  reactions. 
They  form  penta  and  hexa  acetyl  compounds  respectively  with 
acetic  anhydride,  and  the  ring  configuration  is  indicated  by  their 
transformation  into  benzene  derivatives.  Thus,  by  reduction 
with  hydrogen  iodide,  they  both  yield  phenol  and  benzene,  and 
other  products. 

Ketocyclohexane  or  ketohexamethylene  can  be  prepared  from 
calcium  pimelate  by  dry  distillation : 

/CH2.CH2.CO.(X  /CH2.CH2X 

CH2<  >Ca  =  CH2<  >CO  +  CaCO8 

XCH2.CH2.CO.(X  XCH2.CH/ 

Calcium  pimelate  Ketocyclomethylene 

and  this  is  oxidized  by  nitric  acid  to  adipic  acid, 
CH2.CH2.CO.OH 
CH2.CH2.CO.OH 

This  is  a  good  illustration  of  the  relation  of  hydroaromatic  com- 
pounds to  aliphatic  compounds. 

Irone,  the  odoriferous  principle  of  violets,  is  a  hydroaromatic 
ketone  with  the  carbonyl  group  in  a  side  chain.  Its  formula  and 
that  of  the  artificial  oil  of  violets,  ionone,  which  is  made  from 
geranial  (citral)  (p.  87),  differ  only  in  the  position  of  the  double 
bond  in  the  ring: 

1  For  the  optical  activity  of  inosite,  see  Stewart's  "Stereo-Chemistry." 


375  HYDROAROMATIC   HYDROCARBONS 

CH3       CH3 


y 


/\ 

HC        CH.CH:CH.CO.CH3 

II         I 
HC       CH.CH3 

C 

Irone 

CH3       CH3 

V 

C 
/\ 

H2C       CH.CH:CH.CO.CH3 
H2C       C.CH3 


H 

lonone 

The  hydroaromatic  acids  resemble  the  saturated  aliphatic  acids 
having  an  equal  number  of  carbon  atoms.  Thus,  hexahydro- 
benzoic  acid,  CeHn.CO.OH,  is  like  heptylic  acid,  CeHig.CO.OH 
in  its  odor  and  other  characteristics.  It  melts  at  29°,  boils  at 
235°,  and  is  converted  into  benzoic  acid  by  heating  with  anhydrous 
copper  sulphate  to  290°. 

Quinic  acid,  C6H7(OH)4.CO.OH,  a  tetrahydroxyl  acid  which 
is  a  derivative  of  cyclohexane,  occurs  in  cinchona  bark  and  in 
many  other  plants,  and  is  obtained  as  a  by-product  in  the  manu- 
facture of  quinine.  Its  relation  to  the  aromatic  compounds  is 
shown  by  the  following  facts:  When  melted  with  potassium 
hydroxide  it  gives  protocatechuic  acid  (p.  364);  hydrogen  iodide 
reduces  it  to  benzoic  acid;  on  dry  distillation,  it  yields  phenol, 
quinol,  benzoic  acid  and  salicylic  aldehyde.  Quinic  acid  melts  at 
1 6 1. 6°  and  its  solutions  are  levo-rotatory. 


INTRODUCTION    TO    ORGANIC    CHEMISTRY  376 

Hydromellitic  acid,  C6H6(CO.OH)6,  is  of  interest  as  being  the 
compound  whose  discovery  led  Baeyer  to  his  fruitful  investiga- 
tions of  the  hydroaromatic  compounds.  It  is  formed  by  the  re- 
duction of  an  ammoniacal  solution  of  mellitic  acid  with  sodium 
amalgam. 

The  Terpenes 

Terpenes  are  hydrocarbons  which  occur  in  many  plants,  and 
they  are  often  the  chief  constituents  of  the  essential  oils  obtained 
by  distilling  flowers,  fruits,  parts  of  plants,  or  exuded  balsams  and 
oleo-resins  with  steam  (cf.  p.  160).  By  fractional  distillation  of 
the  oils  a  more  or  less  complete  separation  of  the  hydrocarbons 
from  other  constituents  can  be  effected;  but  as  it  is  often  difficult 
to  separate  the  individual  terpenes  in  this  way,  purification  is 
sometimes  accomplished  by  converting  the  terpenes  into  com- 
pounds which  can  be  freed  from  impurities  by  crystallization,  and 
from  which  the  terpenes  can  then  be  recovered. 

Pinene,  doHie,  is  much  the  most  important  of  all  the  many 
terpenes  from  a  practical  point  of  view.  It  is  the  chief  constituent 
of  turpentine  oil.  Turpentine  is  an  oleo-resin  which  exudes  from 
many  coniferous  trees.  It  consists  chiefly  of  a  solution  of  resin 
(colophony)  in  pinene.  On  distillation  with  steam,  turpentine 
oil  comes  over  and  the  resin  is  left  behind.  This  well-known  oil, 
often  called  "turpentine,"  has  a  characteristic  and  pungent  odor, 
which  is  pleasant  when  the  oil  is  freshly  distilled;  but  on  exposure 
to  the  air  the  odor  becomes  unpleasant,  and  the  oil  gradually  grows 
viscid  and  finally  resinous  from  absorption  of  oxygen.  Like  some 
other  substances  which  oxidize  spontaneously  (cf.  p.  345)  the 
turpentine  oil  under  these  conditions  acquires  strong  oxidizing, 
properties,  and  its  value  in  paints  and  varnishes  depends  largely 
on  its  behavior  as  an  oxygen-carrier  to  the  drying  oils  which  are 
used.  Besides  its  employment  in  painting,  it  is  used  as  an  excel- 
lent solvent  for  fats,  resins,  and  caoutchouc.  It  also  dissolves 
sulphur,  phosphorus  and  iodine. 


377  HYDRO  AROMATIC   HYDROCARBONS 

By  fractional  distillation  of  turpentine  oil,  pinene  is  obtained 
nearly  pure.  Pinene  from  French  turpentine  oil  is  levo-rotatory; 
from  American  and  most  other  oils,  dextro-rotatory.  An  optically 
inactive  form  can  also  be  obtained  from  an  addition  product 
which  is  formed  with  nitrosyl  chloride. 

Pinene  is  an  unsaturated  hydrocarbon,  and  is  shown  by  its 
addition  products  with  chlorine  or  bromine  to  have  one  double 
linkage.  It  also  absorbs  dry  hydrogen  chloride  with  the  produc- 
tion of  pinene  hydrochloride,  doHi7Cl,  which  forms  a  white 
crystalline  mass,  melting  at  131°,  and  is  called  "artificial  cam- 
phor" as  it  resembles  camphor  in  appearance  and  odor. 

Pinene  burns  with  a  very  smoky  flame,  and  its  energetic  reac- 
tion with  chlorine  is  shown  by  the  common  lecture  experiment 
of  bringing  a  strip  of  turpentine-soaked  paper  into  this  gas. 

The  evidence  for  the  constitution  of  pinene  and  the  other  ter- 
penes  is  much  too  intricate  for  discussion  here.  Most  of  the 
terpenes  can  be  converted  into  cymene, 


or 

CH(CH3)2 

by  withdrawal  of  two  atoms  of  hydrogen  through  heating  with 
sulphuric  acid  or  iodine.  These  terpenes  are  therefore  hydro- 
aromatic  compounds.  Other  terpenes  are  apparently  open-chain 
compounds  of  the  olefine  series.  Isoprene,  C5H8  (p.  50),  which 
is  obtained  as  a  distillation  product  from  caoutchouc  and  some 
of  the  terpenes,  is  considered  to  be  a  "hemiterpene"  of  this  kind 

CH2 
with  the  formula,         >C.CH  =  CH2. 

CH3 

The  structure  of  pinene  as  shown  in  the  following  formula  is 
dicyclic  —  a  ring  within  the  aromatic  ring. 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  378 

CH2  -  CH  -  CH2 
CH3.C.CH3 

;H  =  c-  -CH 

CH3 

Pinene 

Artificial  Rubber. — The  fact  that  isoprene  can  be  converted  into 
rubber  has  been  mentioned  (p.  50).  The  transformation,  which  is 
one  of  polymerization  or  condensation,  may  be  brought  about  by 
contact  with  hydrochloric  acid  or  certain  other  reagents.  A  small 
amount  of  metallic  sodium  produces  the  change  in  a  few  hours  or 
a  few  days,  according  to  the  temperature.  Methods  for  obtain- 
ing isoprene  cheaply  and  in  sufficient  quantity  for  the  industrial 
manufacture  of  artificial  rubber  have  not  yet  been  found. 

Another  possible  source  for  a  commercial  synthesis  of  rubber  is 
butadiene,  CH2:  CH.CH:CH2,  which  is  condensed  by  sodium  to  a 
product  which,  though  not  identical  with  natural  rubber,  seems 
to  be  superior  to  it  in  some  respects.  Butadiene  is  prepared 
from  normal  butyl  alcohol  which,  in  turn,  may  be  obtained  from 
gelatinized  starch  by  the  action  of  a  special  ferment — acetone 
being  formed  at  the  same  time. 

Camphene,  CioHie,  which  is  the  only  known  solid  terpene,  is 
also  an  unsaturated  compound  whose  exact  constitution  is  not 
yet  known,  though  probably  of  the  same  type  as  that  of  pinene. 
It  is  found  in  two  optically  active  forms  in  French  and  American 
turpentine  and  in  other  vegetable  oils.  It  melts  at  48-50°,  boils 
at  1 60°,  and  is  oxidized  to  camphor  by  chromic  acid. 

In  another  group  of  terpenes  the  members  combine  with  four 
atoms  of  bromine  or  two  molecules  of  a  hydrogen  halide,  and  are 
therefore  represented  with  two  double  bonds. 

Limonene  is  a  representative  of  this  group.  Dextro-limonene 
is  found  in  considerable  quantity  in  orange-peel  oil  and  in 
caraway  oil;  the  levo  form  occurs  in  pine-needle  oil,  and  the 


379  HYDRO  AROMATIC   HYDROCARBONS 

racemic  form  is  obtained  together   with   isoprene   in    distilling 
caoutchouc.     Many  other  oils  also  contain  these  hydrocarbons. 
The  formula  for  limonene  is  given  below  with  that  of  terpinene, 
which  is  a  constituent  of  cardamon  oil. 

CHa  CHa  CHa 

I  I  I 

c  c  c 

/V  /V  /V 

H2C      CH  H2C      CH  H2C      CH 

II  |        |  or  || 

H2C      CH2  HC      CH2  H2C      CH 

CH 


C<f  CH(CH3)2  CH(CH3)2 

XCH3 

Limonene  Terpinene 

Camphors 

Camphors  are  solid  crystalline  substances  which  are  found 
associated  with  terpenes,  and  in  many  essential  oils.  They  have 
characteristic  odors,  sublime  easily,  and  are  volatile  with  steam. 

Camphor,  common  or  Japan  camphor,  CioHieO,  is  obtained  by 
distilling  the  wood  or  leaves  of  the  camphor  tree  with  steam. 
The  camphor  from  this  source  is  dextro-rotatory.  A  levo-rotatory 
form  is  found  in  the  oils  from  certain  plants.  Both  optically 
active  forms  and  a  racemic  form  can  be  obtained  by  oxidation  of 
the  corresponding  borneols  with  nitric  acid,  or  camphenes  with 
chromic  acid. 

The  common  d-camphor  melts  at  178.7°.  Its  uses  in  medicine 
(spirits  of  camphor)  and  in  making  celluloid  are  well  known. 

Camphor  is  a  saturated  compound.  When  distilled  with  phos- 
phorus pentoxide,  camphor  yields  pure  cymene.  By  reduction  it 
is  converted  into  borneol.  It  forms  an  oxime  with  hydroxylamine, 
and  its  oxygen  atom  can  be  replaced  by  two  chlorine  atoms, 
— reactions  which  are  characteristic  of  the  carbonyl  group.  The 


INTRODUCTION    TO    ORGANIC   CHEMISTRY  380 

structure  which  has  been  established  for  camphor  is  that  of  a 
saturated  ketone.  This  is  shown  by  its  formula  which  is  given 
below  together  with  that  of  borneol: 

CH2  —  CH  —  CH2  CH2  —  CH  —  CH2 

I  I 

CH3.C.CH3  CH3.C.CH3 

CH2  —  C CO  CH2  —  C CH.OH 

I  I 

CH3  CH3 

Camphor  Borneol 

Camphor  can  be  made  from  turpentine  oil  by  the  following 
steps:  The  hydrogen  chloride  addition  product  which  pinene 
forms  (artificial  camphor)  is  converted  by  alkalies  into  camphene; 
camphene  unites  with  hydrogen  chloride  to  form  a  compound 
which  is  changed  by  glacial  acetic  acid  into  'isoborneol  acetate, 
CioHi7O.OC.CH3;  this  on  saponification  yields  borneol,  which  is 
oxidized  by  nitric  or  chromic  acid  to  camphor.  This  is  only  one 
of  several  methods  by  which  camphene  hydrochloride  from 
turpentine  oil  has  been  converted  into  camphor.  The  product  is 
identical  with  natural  camphor  in  every  respect  except  that  of 
optical  activity.  The  production  of  artificial  camphor  was 
stimulated  by  the  Russo-Japanese  war,  and  a  good  deal  of  the 
artificial  product  is  now  sold. 

Borneol,  CioHisO,  is  a  secondary  alcohol,  as  the  formula  (above) 
shows.  It  is  obtained  from  certain  trees  of  Borneo  and  Sumatra, 
and  is  found  in  rosemary  and  some  other  oils.  It  is  formed  by 
reduction  of  camphor  in  alcoholic  solution  by  sodium;  but  some 
isoborneol  is  produced  at  the  same  time.  Borneol  has  a  camphor- 
like  odor.  It  melts  at  203°-204°,  boils  at  212°,  and  is  converted 
into  camphor  by  oxidation.  Isoborneol  is  extremely  volatile, 
is  more  soluble  than  borneol,  and  melts  at  212°. 

Fenchone,  CioHisO,  which  occurs  in  fennel  oil,  is  nearly  related 
to  camphor.  It  probably  contains  the  CO  group  in  a  different 
position.  It  melts  at  5-6°. 


HYDRO  AROMATIC   HYDROCARBONS 

Cineol  or  Eucalyptol  is  another  liquid  camphor  which  is  found 
especially  in  oil  of  eucalyptus.  It  boils  at  177°.  Eucalyptol  can 
be  made  from  terpine  hydrate,  a  dihydric  alcohol,  CioHi8(OH)2.- 
H2O,  which  is  readily  obtained  from  turpentine  oil  by  treatment 
with  dilute  acids. 

CH2  -  CH  -  CH.CH3  CH2-CH2 

CH3.C.CH 
CH2  — CH  — CO 


CH3.C<f  \CH.C 


CH2— CH 
-O 


Fenchone  Cineol 

-CH 


^>CH.C^ 


OH 
CH 


CH2— CH 

Terpine 

Menthone  CioHigO,  and  Menthol,  CioH20O,  are  substances  con- 
tained in  peppermint  oil,  menthol  being  the  chief  constituent, 
and  crystallizing  out  of  the  oil  when  it  is  cooled.  Menthol  can 
also  be  made  from  pulegone,  CioHieO,  an  unsaturated  ketone 
which  is  the  chief  constituent  of  oil  of  pennyroyal,  by  reduction 
with  sodium  in  alcoholic  solution.  Menthol  has  a  strong  pepper- 
mint odor,  and  a  pleasant  cooling  taste.  It  is  used  as  a  remedy  for 
neuralgic  headache,  etc.  It  melts  at  43°.  Chemically  it  stands  in 
the  same  relation  to  menthone  that  borneol  does  to  camphor,  one 
being  a  saturated  ketone  and  the  other  a  secondary  alcohol. 

CH.CH3  CHXH3 

/\  /\ 

H2C      CH2  H2C      CH2 

II  II 

H2C      CO  H2C      CHOH 

V  V 

CH:(CH3)2  CH.CH(CH3)2 

Menthone  Menthol 


CHAPTER  XXIX 
NAPHTHALENE  AND  ANTHRACENE 

From  the  higher  boiling  fractions  of  coal  tar  a  number  of  solid 
hydrocarbons  are  obtained  which  have  larger  molecular  weights 
than  benzene  and  a  smaller  proportion  of  hydrogen.  Of  these 
naphthalene  and  anthracene  are  much  the  most  important. 

Naphthalene 

Naphthalene,  Ci0H8,  crystallizes  from  the  fractional  distillate 
of  coal  tar  which  comes  over  between  170°  and  230°  and  is  known 
as  " carbolic  oil"  or  "middle  oil."  Naphthalene  is  present  in 
coal  tar  in  larger  amounts  (5-10  per  cent.)  than  any  other  constit- 
uent, and  forms  an  inexpensive  source  for  the  preparation  of 
valuable  azo  dyes.  After  being  freed  by  pressure  from  most  of 
the  oils  which  cling  to  it,  it  is  purified  by  treatment  with  concen- 
trated sulphuric  acid,  followed  by  distillation  with  steam  or  by 
sublimation. 

Properties. — Naphthalene  crystallizes  in  white  lustrous  plates, 
melts  at  80°  and  boils  at  218°.  It  sublimes  very  readily,  volatiliz- 
ing slowly  at  ordinary  temperatures,  and  has  a  characteristic 
odor  which  is  well-known  from  its  wide  use  in  the  form  of  "moth- 
balls" for  protecting  woolens  and  furs  from  moths.  It  is  insoluble 
in  water,  but  dissolves  freely  in  various  organic  solvents.  It  is 
one  of  the  principal  illuminating  constituents  of  coal  gas,  and 
occasionally  causes  stoppages  in  the  gas  mains  by  crystallizing 
out  of  the  gas  in  cold  weather. 

Naphthalene  is  produced  when  the  vapors  of  many  organic 

382 


3^3  NAPHTHALENE 

compounds  are  passed  through  a  red-hot  tube  (which  explains  its 
presence  in  coal  tar)  and  it  is  present  in  the  products  of  the  dry 
distillation  of  wood. 

Chlorine,  bromine,  and  nitric  acid  act  on  naphthalene  with  the 
production  of  substitution  products;  and  other  groups  such  as 
the  hydroxyl  and  amino  groups  can  be  introduced  by  methods 
used  in  making  benzene  derivatives.  Chlorine  and  bromine  also 
form  addition  products  with  naphthalene.  But  while  naphtha- 
lene and  its  derivatives  are,  in  general  behavior,  like  other  aro- 
matic compounds,  there  are  certain  differences  which  appear  in  a 
readier  activity  of  the  naphthalene  derivatives  as  compared  with 
those  of  benzene. 

The  hydrogen  addition  products — hydronaphthalenes — and 
their  derivatives,  on  the  other  hand,  are,  in  several  cases,  wholly 
aromatic  or  benzene-like  in  their  reactions. 

Structure. — Naphthalene  is  represented  by  the  formula, 

H      H 
C      C 

/S/N 

HC      C      CH 

I        II       I 
HC      C      CH 


C      C 

H      H 

The  evidence  for  this  formula  is  as  follows:  i.  From  the  products 
of  oxidation:  By  active  oxidizing  agents,  naphthalene  is  converted 
into  phthalic  acid  (p.  368) ;  this  indicates  that  it  contains  a  ben- 
zene ring,  and  that  naphthalene  is  an  ortho  di-derivative  of  ben- 
zene. When  nitronaphthalene  is  oxidized,  nitrophthalic  acid 
(i,  2,  3)  is  formed;  but  if  the  nitronaphthalene  is  reduced  to 
aminonaphthalene  and  this  is  oxidized,  unsubstituted  phthalic 
acid  is  the  product,  the  amino  group  being  in  the  part  that  is 
oxidized: 


INTRODUCTION   TO   ORGANIC   CHEMISTRY 


384 


iCO.OH 


XX 

Naphthalene 


N02  NO2 

o 
i    I  .  .  1    — * 

'CO.OH     k     A     J  k     /'CO.OH 

Phthalic  acid         Nitronaphtha-  Nitrophthalic  acid 


NH 


0 


Aminonaphtha- 
lene 


CO.OH 

CO.OH 

Phthalic  acid 


The  same  difference  in  behavior  toward  oxidation  is  observed 
in  other  nitro  and  amino  derivatives.  The  nitro  compounds  are 
stable,  while  the  amino  compounds  are  readily  attacked.  From 
this  we  may  conclude  that  naphthalene  consists  of  two  benzene 
molecules  which  are  coalesced  with  the  dropping  out  of  four  hy- 
drogen atoms,  as  shown  in  the  formula. 

2.  Syntheses  of  naphthalene  can  also  be  made  which  lead  to 
the  same  conclusion  as  to  its  structure.  One  of  these  is  the  follow- 
ing. Phenylisocrotonic  acid,  which  can  be  made  by  heating 
benzaldehyde  with  sodium  succinate  and  acetic  anhydride  (Per- 
kin's  reaction  p.  357)  is  converted  by  continued  boiling  into 
a-naphthol,  from  which  naphthalene  is  readily  obtained: 


iCH:CH.CH2.CO.OH 


Phenylisocrotonic  acid 


-HzO 


OH 

a-Naphthol 


Naphthalene 


Substitution  products  are  obtained  in  greater  numbers  than 
with  benzene,  and  the  number  of  isomers  is  in  accordance  with 
the  possibilities  which  the  naphthalene  formula  indicates.  In  the 
above  formula  where  the  hydrogen-bearing  carbon  atoms  are 


NAPHTHALENE 

numbered,  it  is  seen  that  the  positions  i,  4,  5,  and  8  are  alike,  and 
different  from  2,3,6,  and  7,  all  of  which,  again,  bear  the  same  rela- 
tion to  the  molecule.  A  compound  of  this  formula  should,  there- 
fore, yield  two  and  only  two  monosubstitution  products,  and  this 
is  found  to  be  the  case  with  naphthalene.  These  compounds  are 
distinguished  as  a-derivatives  when  replacement  is  at  i,  4,  5,  or  8, 
and  /3-derivatives  when  in  any  of  the  other  positions. 

When  further  replacements  of  hydrogen  are  made  the  isomeric 
possibilities  are:  For  two  or  six  like  substituents,  10  isomers; 
for  three  or  five,  14 ;  and  for  four,  22.  Two  unlike  atoms  or  groups 
may  give  14  isomers,  and  the  total  possible  number  of  derivatives 
by  direct  replacement  of  hydrogen  has  been  calculated  to  be 
10,766,600. 

While  only  a  very  few  of  the  polysubstitution  products  have 
been  made,  in  no  case  have  more  derivatives  been  obtained  than  is 
predicted  by  the  theory,  and  in  the  case  of  dichlor  substitutions, 
all  ten  have  been  made.  The  positions  of  substituents' may  be 
determined  by  oxidation  into  benzene  derivatives  of  known  posi- 
tions, as  in  the  case  of  nitronaphthalene  above. 

Chlorine  and  bromine  act  on  boiling  naphthalene  with  the  for- 
mation of  a-derivatives.  /3-halogen  derivatives  are  obtained 
indirectly  from  amino  or  sulphonic  derivatives  by  methods  of 
replacement  used  for  the  derivatives  of  benzene.  From  one  to 
four  chlorine  atoms  can  be  introduced  by  the  action  of  chlorine 
alone,  and  in  the  presence  of  a  chlorine  "carrier"  (p.  284)  the 
number  may  be  increased  to  eight,  with  replacement  of  all  the 
hydrogen  atoms. 

Concentrated  sulphuric  acid  at  a  temperature  not  above  80° 
gives  chiefly  a-naphthalene  sulphonic  acid;  at  higher  tempera- 
tures (160°)  the  /3-sulphonic  acid  is  the  sole  product,  since  the 
a-acid  passes  by  intramolecular  rearrangement  into  the  £-acid 
when  heated  to  the  higher  temperature  with  sulphuric  acid.  By 
more  energetic  sulphonation  two  sulphonic  groups  are  introduced, 
the  chief  products  being  the  2,  7,  and  the  2^  6  compounds,  both  of 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  386 

them  di-/3-derivatives.  At  higher  temperatures  and  on  prolonged 
heating,  the  proportion  of  the  2,  6  sulphonic  acid  is  greater. 

Nitric  acid  under  usual  conditions  of  nitration  produces  only 
a-mono-  and  a-dinitro  derivatives.  On  further  nitration  trinitro- 
and  tetranitronaphthalenes  in  many  isomeric  forms  are  obtained. 
A  mixture  of  nitronaphthalenes  is  used  in  making  certain  explo- 
sives, but  their  chief  importance  is  the  preparation  of  naphthyl- 
amines. 

The  formation  of  other  derivatives  is  accomplished  by  the  meth- 
ods used  for  making  benzene  derivatives. 

Naphthols,  the  hydroxyl  derivatives  of  naphthalene,  are  of 
importance  in  the  dye-stuff  industry,  since  they  combine  readily 
with  all  diazo  compounds  to  form  azo-derivatives.  The  hydroxyl 
group  of  the  naphthols  is  replaced  more  easily  than  that  of  phenol ; 
they  give  ethyl-naphthyl  ethers,  C2H6.O.CioH7,  when  heated 
with  alcohol  and  hydrochloric  acid  to  150°;  and  when  heated  with 
zinc  chloride  at  200°,  naphthol  forms  naphthyl  ether,  (CioHy^O, 
(reactions  not  given  by  phenol).  The  naphthols  also  differ  from 
phenol  by  having  much  higher  melting  points  and  being  difficultly 
soluble  in  water. 

The  naphthols  occur  in  coal  tar,  but  in  very  small  quantities, 
and  are  usually  made  from  naphthalene  sulphonic  acids  by  melting 
with  alkalies. 

a-Naphthol,  CioH7.OH,  melts  at  94°  and  boils  at  278°-28o°. 
P-naphthol  melts  at  122°  and  boils  at  285°-286°.  Bleaching 
powder  gives  a  dark  violet  color  with  a-naphthol  in  aqueous  solu- 
tion, and  a  pale  yellow  with  /3-naphthol.  Ferric  chloride  oxidizes 
both  to  dinaphthols,  HO.CioH6.CioH6.OH. 

Dinitro- a-naphthol  (2,  4)  is  obtained  by  the  action  of  dilute 
nitric  acid  on  a-naphthol-disulphonic  acid  (2,  4),  which  effects 
the  replacement  of  the  sulphonic  acid  groups  by  nitro  groups. 
The  sodium  salt  is  known  as  "Martius'  yellow"  which  is  a  direct 
dye  for  wool  and  silk. 

Naphtbylamines,  CioH7.NH2,  can  be  obtained  from  the  nitro- 


NAPHTHALENE 

naphthalenes  by  reduction,  but  are  often  prepared  from  the  naph- 
thols  by  heating  with  ammonium  chloride  and  caustic  soda  or 
with  zinc  chloride  and  ammonia  (cf.  p.  303).  This  reaction  is 
used  especially  for  /3-naphthylamine,  as  the  jS-nitronaphthalene  is 
not  formed  by  direct  nitration,  and,  in  fact,  is  itself  most  read- 
ily made  from  /3-naphthylamine  by  the  diazo  reaction;  while 
/3-naphthol  is  easily  obtained  from  naphthalene  sulphonic  acid. 

The  naphthylamines  are  well-crystallizing  substances  which  can 
be  distilled  without  decomposition.  Their  melting  points  are,  for 
the  a-amine,  50°,  for  the  jS-amine,  112°.  The  ct-amine  has  a  most 
disagreeable  odor,  while  the  other  is  almost  odorless.  They  are 
of  importance  as  sources  (with  benzidine,  p-diamino-diphenyl) 
of  the  Congo  dyes  which  are  substantive  dyes  for  cotton.  Congo- 
red  is  made  by  treating  diazotized  benzidine  with  naphthy- 
lamine-sulphonic  acid,  and  converting  the  product  into  a  sodium 
salt: 

NH2 


Benzidine-diazonium  chloride 


Naphthyl- 
amine  sul- 
phonic acid 


NaS03  •  /SO3Na 


NH  NH2 

Congo-red 

The  acid  of  this  salt  is  blue.  Benzopurpurin  is  made  in  the 
same  general  way,  and  differs  from  Congo-red  by  having  a  methyl 
group  replaced  in  each  of  the  benzene  radicals. 

a-Naphthoquinone,  CioH6O2  (i,  4)  is  formed  as  the  result  of 
direct  oxidation  of  naphthalene  by  chromic  acid  in  glacial  acetic 
acid,  and  is  also  a  product  of  the  oxidation  of  many  a-derivatives. 
It  melts  at  125°  and  resembles  benzoquinone  in  its  yellow  color, 
odor  and  other  properties,  and  is  reduced  to  i,  4-dihydroxy- 
naphthalene  by  sulphurous  acid,  but  the  reduction  does  not  occur 
as  readily  as  that  of  benzoquinone. 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  388 

/8-Naphthoquinone,  Ci0H6O2  (i,  2),  forms  from  its  ether  solu- 
tion red  crystals  which  are  not  volatile,  and  decompose  at  115°- 
120°  without  melting.  By  sulphurous  acid  it  is  reduced  to 
i,  2-dihydroxynaphthalene.  Some  derivatives  of  the  naphtho- 
quinones  are  dyes. 

O  O 


o 


O 

a-Naphthoquinone         /3-Naphthoquinone 

Anthracene 

Anthracene  Ci4Hio,  is  obtained  from  "anthracene  oil"  which  is 
the  highest  boiling  fraction  in  the  distillation  of  coal  tar.  Its 
amount  in  coal  tar  is  only  0.25  to  0.45  per  cent.,  but  it  is  an  im- 
portant substance  as  it  serves  as  the  basis  for  making  the  valuable 
dye  " alizarin"  or  "turkey  red." 

It  forms  white  crystals  which,  when  quite  pure,  have  a  violet 
fluorescence.  It  melts  at  216°  and  boils  at  351°.  It  dissolves 
with  difficulty  in  many  of  the  usual  organic  solvents,  and  is  most 
easily  soluble  in  benzene  and  toluene. 

It  was  discovered  in  coal  tar  in  1832  and  first  called  "paranaph- 
thalene,"  and  later,  anthracene,  from  its  occurrence  in  anthracite 
coal  tar.  In  1868  Graebe  and  Liebermann  found  that  alizarin, 
the  dye  extracted  from  madder,  was  converted  into  anthracene 
by  distillation  with  zinc  dust;  and,  in  the  next  year,  they  synthe- 
sized alizarin  from  anthracene  through  anthraquinone. 

The  structure  of  anthracene  is  established  by  several  synthetical 
methods  of  formation.  The  first  of  these  to  be  carried  out  was 
by  heating  benzylchloride  with  water  at  190°: 

2C6H5.CH2C1     ->    CuHio  +  2HC1  +  H2 

Benzychloride  Anthracene 


389  ANTHRACENE 

This  indicates  that  there  are  two  benzene  rings  in  anthracene 
connected  with  two  additional  carbon  atoms,  as  in 


Another  synthesis  which  leads  to  the  same  conclusion  is  from 
benzene  and  acetylene  tetrabromide  by  the  Friedel-Craft's 
method: 

CHBr2      AlBr, 

2C6H6+  |  > 

CHBr2 

It  is  evident  that,  in  the  Kekule'  formulation,  the  middle  ring 
in  anthracene  cannot  have  the  constitution  of  a  true  benzene  ring. 
The  double  bonds  in  the  two  outer  benzene  rings  may  have  differ- 
ent positions  as  shown  in  the  above  formulas,  and  the  valence 
requirement  in  the  middle  ring  can  be  met  by  one  (or  possibly 
two)  cross  bonds  as  is  indicated,  or  as  in  formula  3.  In  fact, 
anthracene  is  an  unsaturated  compound,  readily  uniting  with 
two  bromine  or  two  hydrogen  atoms  with  the  formation  of 

H  HBr  H  H     H2    H 

H/N/N/NH 

Ci4Hi0Br2,  S|  T  and  Ci4Hi2,  or 

H\AA/H 

H   HBr  H 

The  ortho  position  of  the  linking  carbon  atoms  is  proved  by  the 
synthesis  of  anthracene  from  o-tolylphenylketone  when  heated 
with  zinc  dust: 

xCH3  (i)  /CHv 

C6H4<  »C6H4<    |     >C6H4.  +  H20 

\rn  P.TT,  f*\  Nrw/ 


:O.C6H6  (2) 
The  constitution  of  anthracene  indicates  that  the  number  of 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  390 

substitution  products  should  be  still  greater  than  those  of  naph- 
thalene. There  should  be,  for  instance,  three  monosubstitution 
products,  there  being  three  groups  of  positions,  in  which  the 
members  of  each  group  are  relatively  the  same,  but  differ  from 
those  of  the  other  groups.  These  groups  are,  o:  i,  4,  5}  8;  0:  2,  3, 
6,  757:  9,  10. 

The  halogens  act  on  anthracene  in  much  the  same  way  as  on 
naphthalene.  Concentrated  sulphuric  acid  usually  gives  at  once 
disulphonic  acids.  Nitric  acid,  however,  first  oxidizes  anthracene 
to  anthraquinone,  and  then  converts  this  into  nitro-derivatives 
when  the  acid  is  strong  enough,  or  heated. 

Anthraquinone,  Ci^HgC^,  is  very  important  as  the  source  of 
alizarine.  It  is  a  product  of  the  oxidation  of  anthracene  and  of 
many  derivatives  of  anthracene.  It  is  conveniently  prepared 
by  the  method  used  for  making  naphthoquinone — the  oxidation 
by  chromic  acid  of  the  hydrocarbon  in  glacial  acetic  acid.  It 
forms  yellow  crystals  which  melt  at  284°  and  sublime  in  yellow 
needles,  and  boils  at  382°.  It  is  not  as  volatile  with  steam 
as  other  quinones  are,  lacks  their  pungent  odor,  is  not  reduced  by 
sulphurous  acid,  and  differs  from  them  in  some  other  respects, 
having  rather  the  character  of  a  diketone  than -of  a  quinone. 
Such  a  structure  is  indicated  by  its  synthesis  from  phthalic 
anhydride  and  phenol  when  heated  with  sulphuric  acid,  or  from 
phthalic  anhydride  and  benzene  in  the  presence  of  aluminium 
chloride: 

f~*f\ 

/<-U\  AlCh 

CeH/        >0  +  C6H6  -— >  C6H4<         >C6H4  +  H2O 


anhydride  Anthraquinone 

Anthraquinone  resists  oxidation  to  an  extraordinary  degree. 
From  anthraquinone  only  two  mono-substitution  products  can 
be  obtained,  and  it  is  easily  seen  that  this  exhausts  the  possibilities 
in  tfte  formula: 


39 1  ANTHRACENE 


Alizarin,  C^HeCMOH^,  (i,  2)  was  formerly  obtained  from  its 
glucoside  which  occurs  in  madder-root,  but  is  now  almost  wholly 
prepared  from  anthracene.  Anthraquinone  is  first  made  and 
then  converted  into  monosulphonic  acid  by  heating  with  fuming 
sulphuric  acid  containing  50  per  cent,  of  sulphur  trioxide.  The 
sodium  salt  of  this  sulphonic  acid  is  then  heated  in  a  closed  vessel 
with  sodium  hydroxide  and  potassium  chlorate.  In  this  operation 
the  sulphonic  acid  group  is  replaced  by  hydroxyl,  and  a  second 
hydroxyl  group  formed.  On  acidifying  the  product  of  the  fusion 
with  hydrochloric  acid,  alizarin  is  precipitated: 

NaOH  /CO\ 

C6H3.SO3H   -  >  C6H/        >C6H2(ONa)2 
0 


Anthraquinone  sulphonic  Sodium  salt  of  alizarin 

acid 

By  another  synthesis  of  alizarin  from  phthalic  anhydride  and 
catechol  by  heating  with  sulphuric  acid,  it  is  shown  that  the 
hydroxyl  groups  are  in  the  ortho  position  to  each  other: 

XXX  /OH(i)  /CO.  /OH(i) 

C6H4<        >0  +  C6H4<  ->C6H4<(        >C6H< 

XXX  XOH(2)  XXK  XOH(2) 

Phthalic  anhydride  Catechol  Alizarin 

and  by  a  study  of  the  nitration  products  the  formula  is  proved  to 
be: 

O     OH 

OH 


INTRODUCTION   TO   ORGANIC    CHEMISTRY 


392 


Alizarin  is  only  slightly  soluble  in  water.  From  organic  sol- 
vents it  forms  reddish-yellow  crystals  which  melt  at  289-290°, 
and  sublime  in  orange-colored  needles.  Its  alkali  salts  are  soluble, 
and  give  colored  precipitates  with  the  salts  of  most  other  metals. 
It  is  an  adjective  dye  and  gives  fast  colors  with  mordanted  wool, 
silk,  and  cotton,  forming  " lakes"  of  different  colors  with  the  oxides 
of  the  metals  whose  salts  are  employed  as  mordants.  When  fer- 
ric salts  are  used,  the  color  is  violet-black;  with  chromium,  claret; 
with  aluminium  or  tin,  red,  etc. 

The  formulas  only  of  some  of  the  other  "condensed  ring" 
hydrocarbons  which  are  found  in  anthracite  coal  tar  are  given  here. 
Fluorene  was  named  from  the  violet  fluorescence  it  shows. 


H     H 

"CO" 

"YYT 

HS/H 

H 

Phenanthrene 


CH2-CH2 

HX\X\H 


H\/\/H 
H     H 

Acenaphthene 


H     H2    H 


H  H 

Fluorene 


H 


H 


CHAPTER  XXX 
HETEROCYCLIC  COMPOUNDS 

In  the  chapter  on  the  cycloparaffins  reference  was  made  to  the 
existence  of  compounds  which  contain  a  ring  formation  composed 
of  different  elements,  and  some  illustrations  were  given  of  such 
compounds.  Other  heterocyclic  compounds  have  been  met  with 
in  our  study  of  the  aromatic  substances — chiefly  compounds  in 
which  the  heterogeneous  rings  are  united  with  the  benzene 
nucleus — such  as  acid  anhydrides,  imides,  etc.  In  compounds  of 
this  kind  the  ring  is  usually  broken  readily  by  various  reactions, 
and  does  not  show  the  persistent  integrity  and  property  of 
forming  derivatives  by  replacement  which  distinguish  the  isocyclic 
compounds  which  we  have  studied  in  the  aromatic  group. 

There  are,  however,  a  number  of  compounds  obtained  from 
natural  sources,  and  others  which  have  been  made  in  the  labora- 
tory, which  have  these  properties,  and  are  proved  to  contain  ring- 
nuclei  of  carbon  and  oxygen,  carbon  and  sulphur,  or  carbon  and 
nitrogen.  The  natural  compounds  of  this  group,  whose  structure 
has  been  definitely  established,  are  mostly  obtained  from  coal  tar, 
or  from  the  oil  which  results  from  the  dry  distillation  of  bones, 
and  which  was  formerly  used  in  medicine  under  the  name  of  "Dip- 
pel's  oil."  A  few  of  these  compounds  will  be  briefly  described.  It 
will  be  noticed  that  in  all  of  them  there  are  either  five  or  six  atoms 
in  the  ring-nucleus — the  conditions  for  greatest  stability  according 
to  v.  Baeyer's  strain  theory  (p.  259). 

Furan  or  Furfuran,  C^O,  boiling  at  32°,  is  present  in  pine- 
wood  tar.  A  substance  which  has  the  composition  CBH4O2  and 
the  properties  of  an  aromatic  aldehyde,  was  discovered  in  1849 

393 


INTRODUCTION   TO    ORGANIC   CHEMISTRY  394 

in  the  products  of  the  dry  distillation  of  bran  (furfur).  This 
aldehyde,  whose  formula  may  therefore  be  written  C^aO.CHO, 
is  readily  oxidized  to  pyromucic  acid,  C^sO.CO.OH;  andfuran 
was  first  obtained  by  the  distillation  of  barium  pyromucate.  The 

HC  =  CHk 
formula  assigned  to  f uran  is      I  /  O     This  is   based   on 

HC  =  CH/ 

the  synthesis  of  furan  derivatives,  and  is  supported  by  the 
resemblance  in  properties  between  some  of  these  derivatives  and 
corresponding  aromatic  compounds.  The  oxygen  atom  of  furan 
can  be  shown  to  be  neither  hydroxyl  or  carboxyl  oxygen. 

The  most  important  derivatives  are  the  two  compounds  which 
have  been  mentioned; 

HC  =  CH 


fur  fur  aldehyde, 

HC  =  C  -  CHO 

HC  =  CH 

and  pyromucic  acid,  yO 

HC  =  C.CO.OH 

The  aldehyde  is  formed  when  pentoses  (p.  201)  are  boiled  with, 
dilute  sulphuric  or  hydrochloric  acid.  It  gives  an  intense  red 
dye  when  treated  with  aniline  and  hydrochloric  acid,  and  hence 
its  formation,  as  shown  by  this  test,  is  a  convenient  means  for 
recognizing  pentoses.  It  resembles  benzaldehyde  in  its  reactions 
— thus  with  alcoholic  potash  it  yields  pyromucic  acid  (salt)  and 
furfuryl  alcohol,  C^aO.C^OH.  As  its  name  indicates,  pyro- 
mucic acid  was  originally  obtained  by  dry  distillation  of  mucic  acid 
(p.  206). 

Thiophene,  C4H4S,  gives  a  blue  color  with  isatin  (an  oxidation 
product  of  indigo)  and  sulphuric  acid  (indophenine  reaction). 
This  reaction  was  thought  to  be  characteristic  of  benzene,  and 
the  failure  of  the  test  in  some  benzene  which  had  been  made  from 


395  HETEROCYCLIC   COMPOUNDS 

benzoic  acid  led  to  the  discovery  of  thiophene  in  commercial 
benzene  by  V.  Meyer  (1883).  Thiophene  is  present  in  coal-tar 
benzene  to  the  amount  of  about  0.5  per  cent.  It  can  be  separated 
from  benzene  by  the  fact  that  its  sulphonic  acid  is  formed  more 
readily  than  that  of  benzene.  By  heating  with  water  under 
pressure  thiophene  is  regenerated  from  its  sulphonic  acid.  Methyl 
derivatives  of  thiophene  are  found  in  coal-tar  toluene,  xylenes,  etc. 

Thiophene  is  a  colorless  liquid  boiling  at  84°,  and  cannot  be 
separated  from  benzene  by  distillation.  It  is  somewhat  heavier 
than  water  and  has  no  characteristic  odor.  Its  aromatic  character, 
as  shown  by  its  reactions,  is  pronounced. 

Thiophene  has  been  synthesized  by  heating  sodium  succinate 
with  phosphorus  trisulphide: 

CH2.C£).ONa          HC  =  CH 

P»St  \ 

S 


CH2.CO.ONa          HC  =  CH 

Sodium  succinate  Thiophene 

Its  structure  as  given  in  the  above  formula  is  inferred  from  this 
and  other  syntheses,  and  is  seen  to  be  of  the  same  type  as  that  of 
furan,  with  sulphur  in  place  of  oxygen. 

Pyrrol,  C^sN,  is  a  colorless  oil  which  has  an  odor  resembling 
that  of  chloroform,  and  which  boils  at  131°.  It  is  found  in  coal 
tar  and  bone  oil.  Its  name  is  from  its  property  of  giving  a  bright 
red  (irvppos)  color  to  a  pine  shaving  moistened  with  hydrochloric 
acid.  It  can  be  synthesized  by  distilling  succinimide  with  zinc 
dust: 

CH2.CO  HC  =  CH 


\ 


NH 


\ 


CH2.CO  HC  =  CH 

Succinimide  Pyrrol 


NH 


This  and  other  syntheses,  and  its  reactions  have  led  to  the 
establishment  of  the  structure  shown  above,  which  makes  it  a 


INTRODUCTION   TO   ORGANIC   CHEMISTRY  396 

secondary  amine.  It  is,  however,  only  a  weak  base,  dissolving 
slowly  in  dilute  acids  in  the  cold,  and  it  is  changed  by  strong  acids 
to  a  resin.  As  a  consequence,  no  sulphonic  acids  can  be  obtained, 
and  nitro  derivatives  only  by  an  indirect  method. 

Pyrrol  shows  more  striking  analogies  to  the  phenols  than  to  the 
aromatic  hydrocarbons.  The  imide  (NH)  hydrogen,  like  the 
phenol  hydroxyl  hydrogen,  can  be  replaced  by  potassium  forming 
potassium  pyrrol,  C^tNK,  and  the  hydrogen  atoms  of  the  CH 
groups  are  replaced  by  halogens  with  great  readiness.  It  also 
couples  directly  with  diazonium  salts  giving  azo  dyes.  Ho- 
mologous pyrrols  occur  in  bone  oil,  and  can  be  made  by  passing 
vapors  of  pyrrol  and  alcohols  over  zinc  dust.  Pyrrol  derivatives 
are  very  widely  distributed  in  nature.  The  pyrrol  ring  is  found 
to  be  present  in  certain  alkaloids,  and  haemoglobin  (the  red  color- 
ing matter  of  the  blood)  and  chlorophyll  are  to  be  considered  as 
derivatives  of  methyl-propyl  pyrrol. 

Pyridine,  CsHj^N,  a  liquid  of  very  disagreeable  odor,  boiling 
at  115°,  can  be  obtained  from  the  "light  oil"  distillate  from  coal 
tar,  and  also  from  bone  oil.  Syntheses  of  pyridine  and  its  reac- 
tions indicate  that  it  may  be  regarded  as  benzene  with  one  CH 
group  replaced  by  a  nitrogen  atom 

N 

HC      CH 

II        I 
HC      CH 

\/ 

CH 

It  is  a  very  stable  compound,  behaving  very  much  like  benzene, 
but  it  cannot  be  nitrated,  and  gives  sulphonic  and  halogen  deriva- 
tives with  greater  difficulty  than  benzene.  It  is,  however,  easily 
reduced  by  sodium  and  alcohol,  and  adds  six  hydrogen  atoms  to 
form  piperidine, 


397  HETEROCYCLIC  COMPOUNDS 


<2.  —       2\ 
>NH 
CH2.-CH/ 

a  liquid  of  pepper-like  odor,  boiling  at  106°,  which  is  also  obtained 
from  pepper.  Pyridine  is  a  tertiary  amine  as  its  formula  shows. 
Its  basic  properties  are  stronger  than  those  of  pyrrol,  and  about 
the  same  as  aniline,  its  solutions  being  weakly  alkaline,  and  fairly 
stable  salts  being  formed. 

Homologues  of  pyridine  occur  with  it,  and  can  also  be  synthe- 
sized. The  side  chains  of  these  homologues  are  oxidized  to  car- 
boxyl  groups,  as  in  the  case  of  toluene,  etc.  One  of  them  is  called 
nicotinic  acid  because  it  is  also  a  product  of  the  oxidation  of  the 
alkaloid  nicotine.  Pyridine  and  its  homologues,  the  pyridine 
bases,  are  found  to  occur  in  the  products  of  distillation  of  almost 
all  kinds  of  nitrogenous  substances;  and  among  the  naturally 
occurring  members  of  the  pyridine  group  are  several  important 
alkaloids. 

Quinoline,  C9H7N,  which  occurs  in  coal  tar  and  bone  oil,  is  a 
liquid  boiling  at  239°.  It  has  been  synthesized  by  methods  which 
establish  its  structure  as  a  condensation  of  benzene  with  pyridine: 

CH  N 


HC      C      CH 

I       II        I 
HC      C      CH 


C      C 
H     H 

Its  name  is  from  its  discovery  as  a  product  of  the  distillation  of 
quinine.  Quinoline  is  a  tertiary  base  which  forms  crystalline 
and  very  soluble  salts  with  one  equivalent  of  acids.  It  forms 
derivatives  like  other  aromatic  compounds.  It  has  a  penetrating 
odor  and  a  strong  antiseptic  action.  When  oxidized  by  potassium 
permanganate  the  benzene  ring  breaks  down  with  the  production 
of  carboxyl  groups  and  the  formation  of  quinolinic  acid: 


INTRODUCTION    TO    ORGANIC    CHEMISTRY  398 

N 

/\ 

HC       C  -  CO.OH 

II         I 
HC       C  -  CO.OH 

\S 

CH 

This  when  heated  is  decomposed  into  nicotinic  acid  and  when  dis- 
tilled with  lime  gives  pyridine.  Quinoline  adds  hydrogen  atoms 
easily,  which  go  almost  exclusively  into  the  pyridine  ring. 

An  isomer  of  quinoline,  called  isoquinoline,  also  occurs  in  coal 
tar.  It  melts  at  21°  and  boils  at  237°.  The  nitrogen  atom  in 
isoquinoline  is  not  directly  united  to  the  benzene  nucleus  as  in 
quinoline,  but  occupies  what  in  naphthalene  is  called  the  /3-posi- 
tion.  Isoquinoline  is  more  basic  than  quinoline,  and  absorbs 
carbon  dioxide  from  the  air. 

Indigo,  CieHioN2O,  is  a  compound  containing  two  heterocyclic 
groups,  as  shown  in  the  following  formula  which  is  seen  to  contain 
two  pyrrol  rings: 

H  H 

C  H  H  C 

/\          I  I  /\ 

HC      C  — NX  /N  —  C        CH 


HC      C—  C'  C  —  C        CH 


y 


O  O  C 

H  H 

The  history  of  the  elucidation  of  the  structure  of  indigo  is  very 
interesting.1  The  following  is  a  brief  summary.  In  1826  aniline 
was  obtained  from  indigo  by  dry  distillation.  In  1841,  anthrani- 
lic  acid  (p.  360)  was  found  to  be  a  product  of  its  oxidation.  Later, 
it  was  found  that  when  indigo  was  oxidized  by  nitric  acid 

1  See  Sidgwick's  "Organic  Chemistry  of  Nitrogen," 


399  HETEROCYCLIC   COMPOUNDS 

was  produced,  whose  constitution  was  afterward  established  as 

xco\ 

C6H4<f         /CO,  and  which  was  synthesized  from  o-nitrophenyl- 
acetic  acid  through  oxindol: 

yCH2.CO.OH        H  /CH2.CO.OH  -H,o 

4\  -  >  CeH4<\  -  > 

XN02  XNH2 

o-Nitrophenylacetic  o-Amidophenylacetic 

acid  acid 


/CHzv  o  /CO\ 

4<          >CO   -  >C6H/        >CO 
NNH'  XNH/ 


C6H 

Oxindol  Isatin 

In  1870  indigo  was  made  from  isatin  by  treatment  with  phos- 

phorus pentachloride,  followed  by  reduction.    This  was  the  first 

true  synthesis  of  indigo.    Its  structure,  however,  was  not  yet 

established. 

The   heterocyclic   hydrogen   compound  of  which   isatin  is  a 

/CH. 

derivative  is   indol,  CeH4<(          /CH,   which  is  obtained  from 

/ 


indigo  or  oxindol  on  distillation  with  zinc  dust,  and  can  be 
synthesized  in  several  ways.  It  may  be  regarded  as  the  mother 
substance  of  indigo  and  its  derivatives.  It  is  a  crystalline  solid, 
melting  at  52°  and  boiling  at  245°.  The  presence  of  the  pyrrol 
ring  in  indol  is  evident  in  its  formula.  It  resembles  pyrrol  in 
many  respects  and  gives  the  pyrrol  reaction  with  a  pine  shaving. 
It  was  shown  that  isatin  could  be  reduced  by  successive  steps 
to  indol  without  the  production  of  indigo: 

P  O  CH.OH 

C6H4</       N>CO-»C6H 

NNH/ 

Isatin  Dioxindol  Oxindol 


INTRODUCTION   TO    ORGANIC  CHEMISTRY  400 

C6H4< 


Indol 

In  these  ways  the  relation  of  indigo  to  indol  was  determined 
and  its  structure  was  finally  established  by  a  synthesis  by 
Baeyer;  in  1882  of  o-dinitro-diphenyl-diacetylene, 

c  =  c  -  c  =  Cv 

CeH4<f  yCeH4,  which  on  reduction  yields  indigo. 

XN02  NO/ 

Many  other  syntheses  of  indigo  have  been  effected  since  its 
structure  became  known,  but  only  after  twenty  years  of  continuous 
research  was  a  process  found  by  which  synthetic  indigo  could  be 
manufactured  at  a  price  which  could  compete  with  the  natural  pro- 
duct. There  are  now  several  rival  processes  in  the  field,  of  which 
the  most  successful  at  present  is  that  of  Heumann.  This  is,  in 
brief,  as  follows:  Naphthalene  is  oxidized  to  o-phthalic  acid  by 
heating  with  fuming  sulphuric  acid  (made  by  the  contact  process)  ; 
phthalic  acid  is  converted  into  aminobenzoic  acid  (anthranilic 
acid,  p.  360);  this  is  then  condensed  with  chloracetic  acid  to 
phenyl-glycine-o-carboxylic  acid,  which  on  fusion  with  potash 
gives  indoxyl.  When  the  mass  containing  indoxyl  is  treated  with 
water  and  exposed  to  the  air,  oxidation  to  indigo  takes  place. 
The  more  important  steps  are: 

/CO.OH  /NH2 

C6H4.C4H4    -»C6H4<  -»C6H4<  + 

\CO.OH  XCO.OH 

Naphthalene  o-Phthalic  acid  Aminobenzoic  acid 

XNH.CH2.CO.OH 
CH2C1.CO.OH    ->C6H< 

XXXOH 

Chloracetic  acid  Phenylglycine 

o-carboxylic  acid 


V 
CH2   ->  C6H  C  =  C  >C6H4 

XCCK  XCCK 

Indoxyl  Indigo 


401  HETEROCYCLIC  COMPOUNDS 

The  commercial  success  of  the  process  depends  largely  upon  (i) 
the  cheapness  of  naphthalene,  which  is  produced  from  coal  tar 
in  great  excess  of  the  demand,  and  (2)  on  the  comparatively 
inexpensive  production  of  fuming  sulphuric  acid,  for  oxidation  of 
the  naphthalene,  by  the  contact  process,  and  the  fact  that  the 
sulphur  dioxide  which  results  from  the  oxidation  is  readily 
reoxidized  by  this  same  process. 

Another  synthesis  that  runs  on  simpler  lines  and  gives  a  good 
yield  of  indigo  is  now  worked  in  England.  The  starting  point 
here  is  aniline,  which  is  treated  with  chloracetic  acid  with  the 
production  of  phenylglycine,  C6H5NH.CH2.CO.OH.  This  when 
heated  with  sodium  amide,  or  sodium  in  the  presence  of  ammonia, 
is  dehydrated  with  the  formation  of  indoxyl  which  gives  indigo 
on  oxidation  by  a  current  of  air. 

Natural  indigo  occurs  as  indican  (probably  a  glucoside  of  in- 
doxyl) in  the  indigo  plant.  It  is  obtained  by  immersing  the  leaves 
in  water  and  stirring  to  promote  atmospheric  oxidation.  An 
enzyme  present  in  the  leaves  breaks  up  the  indican  into  glucose 
and  indoxyl,  and  the  latter  is  oxidized  to  indigo. 

Indigo  is  a  dark  blue  substance,  insoluble  in  most  ordinary  sol- 
vents, but  dissolving  in  aniline,  melted  paraffin,  etc.,  and  crys- 
tallizes from  these  solutions.  It  forms  a  dark  red  vapor  when 
heated,  and  under  diminished  pressure  can  be  sublimed  without 
decomposition.  In  dyeing  it  is  either  converted  into  a  soluble 
disulphonic  acid,  or  it  is  reduced  to  the  leuco-base,  indigo  white 
(probably  a  di-indoxyl),  by  glucose  in  alkaline  solution.  In  the 
former  case  it  dyes  directly;  in  the  latter,  the  indigo  white  depos- 
ited on  the  fibres  is  oxidized  to  indigo  on  exposure  to  the  air. 


CHAPTER  XXXI 
ALKALOIDS— PROTEINS 

The  alkaloids  are  organic  bases  which  occur  in  plants.  Most  of 
them  have  a  powerful  physiological  action  and  many  are  ex- 
tremely poisonous.  They  were  long  considered  to  be  substituted 
ammonias  or  ammonium  bases.  But  while  this  is  true  of  some  of 
them,  such  as  muscarine  and  amanitine,  which  occur  in  toad-stools, 
most  of  the  important  alkaloids  are  now  known  to  be  heterocyc- 
lic  compounds  which  contain  at  least  one  nitrogen  atom  in  their 
nucleus,  and  may  therefore  be  regarded  as  derivatives  of  pyrrol, 
pyridine,  quinoline,  or  iso-quinoline.  Some  of  them  have  been 
synthesized. 

Most  of  the  alkaloids  are  crystalline  solids,  only  a  few,  such  as 
nicotine  and  coniine,  are  liquids.  They  have  a  bitter  taste,  are 
mostly  insoluble  in  water,  but  dissolve  in  alcohol,  and  to  some 
extent  in  ether.  They  have  an  alkaline  reaction,  dissolve  in  acids 
forming  salts  which  are  often  well-crystallizing  compounds. 

Most  of  the  alkaloids  are  precipitated  from  their  acid  solutions 
by  certain  "general  alkaloid  reagents":  tannic,  picric,  molybdic, 
phosphomolybdic,  and  phosphotungstic  acids,  potassium  mercuric 
iodide,  etc.  These  precipitates  are  decomposed  by  alkalies  with 
liberation  of  the  alkaloids.  Many  of  the  alkaloids  are  optically 
active  and  almost  all  of  them  are  levo  rotatory.  The  alkaloids  are 
often  identified  by  color  reactions. 

A  few  of  the  important  alkaloids  are  here  briefly  described. 

Coniine,  CsHvN,  occurs  in  hemlock,1  and  was  the  first  alkaloid 

1The  European  poison  hemlock,  not  the  American  hemlock,  which  is 
a  species  of  pine. 

402 


403  ALKALOIDS 

to  be  synthesized.  Its  structural  formula  shows  the  pyridine 
ring,  and  that  it  is  more  directly  a  derivative  of  piperidine  (p. 
396),  being  a-propylpiperidine, 

H2 
C 


H2C      CH2 

I        I 
H2C       CH.CH2.CH2.CH2 


Y 


H 

It  is  one  of  the  few  dextro  rotatory  alkaloids.     Conime  is  a  color- 
less liquid  boiling  at  167°. 

Nicotine,  doH14N2,  is  also  a  liquid  alkaloid,  obtained  from 
tobacco.  It  boils  at  247°.  On  oxidation  with  permanganate  it 
yields  nicotinic  acid  (p.  397),  and  therefore  contains  the  pyridine 
ring.  The  pyrrol  nucleus  is  also  present,  the  formula  for  nicotine 
being, 


It  is  exceedingly  poisonous,  but  when  tobacco  is  burned  most 
of  the  nicotine  is  volatilized  or  destroyed. 

Nicotine  from  tobacco  is  levo  rotatory,  but  both  optical  forms 
have  been  obtained  from  the  synthetical  product.  The  two  forms 
produce  somewhat  different  physiological  effects.  4 

Atropine,  Ci7H23NO3,  like  all  alkaloids  which  contain  oxygen,  is 


INTRODUCTION   TO    ORGANIC    CHEMISTRY  404 

a  solid.  It  melts  at  115°.  It  is  the  principal  alkaloid  of  bella- 
donna or  deadly  nightshade,  and  is  the  most  important  alkaloid 
of  the  nightshade  family.  Its  use  by  oculists  to  dilate  the  pupil 
of  the  eye  is  well  known.  The  complicated  structure  of  atropine 
has  been  determined. 

Cocaine,  Ci7H2iNO4,  from  coca-leaves,  is  much  used  as  a  local 
anesthetic.  It  is  related  in  structure  to  atropine.  When  heated 
with  hydrochloric  acid  it  gives  benzoic  acid,  methyl  alcohol,  and 
ecgonine,  a  carboxylic  acid  of  tropine,  a  substance  which  is  ob- 
tained from  atropine  by  hydrolysis. 

Morphine,  CiyHigNOs,  is  the  chief  alkaloid  of  opium,  which  is 
the  dried  juice  of  the  seed  capsules  of  a  variety  of  poppy. 

Strychnine,  C2iH22N2O2,  andbrucine,  C23H26N2O4,  are  obtained 
from  the  Strychnos  nux  wmica. 

Quinine,  C2oH24N2O2,  is  the  most  important  of  the  twenty-four 
alkaloids  which  have  been  obtained  from  "Peruvian  bark." 
Quinine  melts  at  177°.  Its  structure  is  evidently  very  complicated 
and  has  not  been  definitely  established.  It  is  known  to  contain 
the  quinoline  ring.  Dilute  solutions  of  its  salts  show  a  fine  blue 
fluorescence.  It  is  usually  employed  in  medicine  in  the  form  of 
its  soluble  sulphate. 

Proteins 

Among  the  organic  substances  present  in  animals  and  plants, 
the  compounds  called  proteins  (irpureLov,  pre-eminent)  are  of 
very  great  importance.  In  animals  by  far  the  larger  part  of  the 
tissue  solids  is  generally  protein,  and  protein-containing  foods  are 
absolutely  essential  for  their  nourishment. 

Proteins,  like  the  fats  and  carbohydrates,  are  found  only  in 
living  matter  or  as  products  of  living  matter.  The  proteins  in 
living  matter  are  such  a  mixture  of  different  kinds,  and  they  are  in 
general  so  unstable,  that  the  extraction  of  individual,  pure  pro- 
teins is  usually  very  difficult.  In  a  few  instances  proteins  that 


4°5  PROTEINS 

are  apparently  pure  have  been  separated  from  animal  tissues. 
Plants,  unlike  animals,  store  proteins  as  a  reserve  in  their  seeds, 
and  these  proteins  are  very  stable.  From  seeds  and  nuts,  there- 
fore, proteins  may  be  obtained  with  comparative  ease  by  extrac- 
tion with  water,  alcohol,  or  a  solution  of  salt. 

The  composition  of  the  proteins  varies  considerably.  They  all 
contain  carbon,  hydrogen,  nitrogen,  and  oxygen,  usually  sulphur, 
and  sometimes  also  phosphorus  and  iron.  Typical  proteins  con- 
sist of  carbon,  about  52  per  cent.;  hydrogen,  7  per  cent.;  nitrogen, 
15  per  cent.;  oxygen,  23  per  cent.;  sulphur,  0.5  per  cent.;  phos- 
phorus, 0.3-5  Per  cent- 

Many  proteins  are  colloids,  and  advantage  is  taken  of  this 
property  in  separating  them  from  salts  and  other  crystalloids  by 
diffusion  through  membranes.  Many  of  them  occur  naturally  in 
crystalline  form  in  seeds  and  nuts,  and  have  been  crystallized  in 
the  laboratory.  Their  solutions  are  optically  active  and  most  of 
them  are  levo-rotatory.  They  all  have  a  more  or  less  amphoteric 
character.  In  aqueous  solution  they  are  coagulated  by  boiling  or 
on  the  addition  of  strong  alcohol  or  inorganic  acids.  Insoluble 
compounds  are  formed  with  solutions  of  salts  of  most  of  the  heavy 
metals,  and  also  with  weak  acids  such  as  tannic,  picric,  and  phos- 
photungstic  acids. 

We  owe  our  present  knowledge  of  these  exceedingly  complex 
substances  largely  to  the  work  of  Kossel  and  of  Emil  Fischer.  It 
has  been  found  that  the  final  products  of  the  hydrolysis  of  proteins 
are  ammo  acids  (p.  252),  of  which  glycine  or  aminoacetic  acid  is 
the  simplest  representative.  Intermediate  compounds  called 
polypeptides  are  formed  which  are  condensation  products  of 
various  amino  acids,  such  as  glycylglycine,  NH2CH2CO.NH. 
CH2.CO.OH,  from  two  molecules  of  glycine. 

From  these  facts  and  from  other  considerations  the  conclusion 
was  drawn  that  the  proteins  are  largely  made  up  of  a-amino  acids 
linked  through  their  amino  and  carboxyl  groups,  the  number  and 
kind  of  these  amino  acids  being  variable  in  different  proteins. 


INTRODUCTION    TO    ORGANIC   CHEMISTRY 


406 


This  view  is  confirmed  by  the  synthesis  of  more  than  one  hundred 
complex  polypeptides  that  have  the  properties  of  natural  proteins 
after  their  modification  by  contact  with  reagents.  One  of  the 
most  complex  of  these  synthesized  substances  contained  eighteen 
amino  acid  groups  and  had  a  molecular  weight  of  1213. 

The  classification  of  the  proteins  adopted  by  the  American 
Society  of  Biological  Chemists  is  as  follows. 

I.  Simple  Proteins.     Albumins,  Globulins,  Glutelins,  Prolamins, 
Albuminoids,  Histones,  Protamins. 

II.  Conjugated  Proteins.     Nucleoproteins,  Glycoproteins,  Phos- 
phoproteins,  Haemoglobins,  Lecithoproteins. 

III.  Derived  Proteins.     Primary  derivatives:  Proteans,  Meta- 
proteins,    Coagulated    Proteins.     Secondary    derivatives:    Pro- 
teoses,  Peptones,  Peptides. 

The  simple  proteins  and  the  conjugated  proteins  are  all  sub- 
stances that  are  supposed  to  exist  in  the  tissues  and  juices  of  ani- 
mals and  vegetables.  The  conjugated  proteins  consist  of  one  or 
more  molecules  of  albumin  associated  with  some  other  substance 
of  a  different  nature,  such  as  sugar.  They  do  not  always  contain 
sulphur,  but  phosphorus  is  a  constituent  of  many  of  them.  Sev- 
eral, such  as  haemoglobin,  the  red  coloring  matter  of  blood, 
contain  iron. 

The  derived  proteins  represent  the  first  stages  in  the  process  of 
decomposition  that  the  proteins,  simple  or  conjugate,  undergo  in 
contact  with  almost  any  reagent.  The  solubility  is  affected  by 
the  simple  operation  of  diffusion;  and  contact  with  acids,  alkalies, 
or  metallic  salts  causes  incipient  hydrolysis. 

While  the  exact  steps  that  lead  to  the  formation  of  the  natural 
proteins  are  obscure,  it  is  probable  that  they  are  produced  by  the 
condensation  of  decomposition  products  of  the  carbohydrates  with 
ammonia. 

A  few  examples  of  the  variety  that  proteins  offer  may  be  of 
interest.  White  of  egg  and  serum  albumin  are  illustrations  of  the 
albumins,  which  are  the  best  known  of  the  proteins;  to  the  albu- 


407  PROTEINS 

minoids  belong:  collagen,  the  chief  constituent  of  connective  tis- 
sue, bone,  and  cartilage,  which  yields  gelatin  or  glue  by  partial 
hydrolysis;  elastin  in  the  elastic  tissue  of  ligaments  and  walls  of 
arteries;  and  keratin  which  contains  sulphur  —  up  to  5  per  cent., 
and  is  the  principal  constituent  of  epidermis,  hair,  feathers,  and 
horny  tissues.  An  example  of  a  phosphoprotein  is  casein,  chief 
nitrogeneous  constituent  of  milk,  which  is  coagulated  by  rennet. 
The  molecular  weights  of  the  proteins  are  not  accurately  known, 
but  they  are  certainly  very  large.  Osborne  has  calculated  the 
molecular  weights  in  a  number  of  instances  from  the  percentage  of 
sulphur  present,  on  the  assumption  that  there  are  two  or  more 
atoms  of  sulphur  in  the  molecule.  This  assumption  is  based  on 
the  fact  that  cystine,  whose  molecule  is  known  to  contain  two 
atoms  of  sulphur,  is  a  constituent  of  many  of  these  proteins.  The 
following  is  an  illustration  of  the  method  of  calculation.  A  globin 
has  the  percentage  composition:  C  =  54.98,  H  =  7.20,  N  = 
16.89,  O  =  20.51,  S  =  0.42.  If  there  are  two  atoms  of  sulphur 
in  the  molecule,  weighing  64,  the  weights  in  atomic  weight  units 
of  each  of  the  other  elements  is  readily  calculated,  and  the  sum  is 
the  molecular  weight.  From  these  figures  an  empirical  formula 
may  be  obtained.  In  the  case  of  this  globin  the  figures  for  the 
molecular  weight  are  15,274,  and  the  formula  is: 


Similar  figures  are  obtained  for  other  proteins  by  this  and  other 
methods. 


INTRODUCTION   TO    ORGANIC    CHEMISTRY 


408 


Specific  Rotations  of  Some  Optically  Active  Substances 

The  angle  through  which  plane  polarized  light  is  rotated  by  solutions  of 
optically  active  substances  depends  on  the  concentration,  the  length  of  solu- 
tion through  which  the  light  passes,  the  wave-length  of  the  light,  and  the 
temperature,  as  well  as  on  the  nature  of  the  substance.  The  Specific  Rota- 
tion is  the  rotation  produced  with  yellow  (sodium)  light  in  passing  through 
one  decimeter  of  a  solution  that  has  one  gram  of  substance  in  each  cubic 
centimeter,  at  2o°C. 

In  the  following  formula  [a]  is  the  specific  rotation,  a  the  observed  angle  of 
rotation,  I  the  length  of  the  solution  in  decimeters,  v  the  volume  in  cubic 
centimeters,  and  w  the  weight  of  substance  in  the  solution.  D  indicates  that 
the  measurement  is  made  with  sodium  light. 


In  the  case  of  liquid  substances  examined  without  a  solvent,  the  formul- 


becomes  [a]D  —    -j  in  which  d  is  the  density. 


Arabinose 
Xylose 
Rhamnose 
Glucose 
Fructose 
Invertose 
Galactose 
Mannose 
Sorbose 

C6(CH3)H9O6 
C6Hi206 
C6H12O6 
C6H12O6 
C6H1206 

C6H12O6 

+  105 
+  19 
+9 
+  52 
-93 
-19 
+81 
+  H 
—  42 

.0 

.0 
.0 

•  7 
.8 
.6 
.0 

.0 
.0 

Sucrose             Ci2H22Ou 
Lactose             Ci2H22Ou 
Maltose             Ci2H22On 
Raffinose           CisH^Oie 
Tartaric  acid 
Saccharin 
Quinine  sulphate 
Nicotine 
Camphor  (in  alcohol) 
Oil  of  turpentine 

MD 
+66. 

+52. 
+  138. 
+104. 

+15. 

+88. 
-213. 
-77. 
+56. 
+36. 

5 

5 
o 

0 

61 

7 
7 

0 

15 

o 

lonization  Constants  of  Some  Organic  Acids  and  Bases 


Monobasic  Acids 
Formic 
Acetic 
Glycollic 
Glyoxylic 
Chloracetic 
Dichloracetic 
Trichloracetic 


k  X 


HCO.OH 

CH3.CO.OH 

CH2OH.CO.OH 

CHO.CO.OH 

CH2C1.CO.OH 

CHC12.CO.OH 

CCls.CO.OH 


21.4 
1.85 
15-0 
50.0 


5,000.0 
30,000  .  o 


409    IONIZATION  CONSTANTS  OF  ORGANIC  ACIDS  AND  BASES 


Propionic 

Lactic 

/3-Hydroxypropionic 

Glyceric 

a-Chlorpropionic 

/3-Chlorpropionic 

Butyric 

7-Oxybutyric 

a-Chlorbutyric 

/3-Chlorbutyric 

7-Chlorbutyric 

Fumaric 

Maleic 

Valeric 

Benzoic 

o-Oxybenzoic 

wi-Oxybenzoic 

^-Oxybenzoic 

Dioxybenzoic 

Dioxybenzoic 

Dioxybenzoic 

Dioxybenzoic. 

0-Nitrobenzoic 

w-Nitrobenzoic 

0-ChJorbenzoic 

w-Chlorbenzoic 

^-Chlorbenzoic 

Cinnamic 

Sulphanilic 

Anthranilic 

Dibasic  Acids 
Carbonic 
Oxalic 
Malonic 
Tartronic 
Succinic 
Malic 
Tartaric 
0-Phthalic 
m-Phthalic 


CH8.CH2.CO.OH 

CH3.CHOH.CO.OH 

CH2OH.CH2.CO.OH 

CHaOH.CHOH.CO.OH 

CH3.CHC1.CO.OH 

CH8C1.CH2.CO.OH 

CH3.CH2.CH2.CO.OH 

CH2OH.CH2.CH2.CO.OH 

CH3.CH,.CHC1.CO.OH 

CH3.CHC1.CH2.CO.OH 

CH2.C1.CH2.CH2.CO.OH 

CO.OH.CH:CH.CO.OH 

CO.OH.CHrCH.CO.OH 

CH3.CH2.CH2.CH2.CO.OH 

C6H6.CO.OH 

C6H4(CO.OH)(OH)  i,  2 

C6H4(CO.OH)(OH)  i,  3 

C6H4(CO.OH)(OH)  i,  4 

C6H3.(CO.OH)(OH;2  1,2,3 

C6H3.(CO.OH)(OH)2  i,  2,  4 

C6H3.(CO.OH)(OH)2  i,  2,  6 

C6H3.(CO.OH)(OH)2  i,  3,  4 

C6H4.(CO.OH)NO2  i,  2 

C6H4.(CO.OH)NO2  i,  3 

C6H4.(CO.OH)C1  i,  2 

C6H4.(CO.OH)C1  i,  3 

C6H4.(CO.OH)C1  i,  4 

C6H6.CH:CH.CO.OH 

NH2.C6H4.SO3H 

C6H4.(CO.OH)NH2  i,  2 

CO(OH)2 

(CO.OH)2 

CH2(CO.OH)a 

CHOH(CO.OH)2 

CO.OH.CH2.CH2.CO.OH 

CO.OH.CHOH.CH2.CO.OH 

CO.OH(CHOH)2CO.OH 

C6H4(CO.OH)2  i,  2 

C6H4(CO.OH)i  i,  3 


1.4 

13-8 

3-i 

23.0 

147.0 
8-5 
i-S 
1.9 

139.0 
8-94 
3-o 

100.  o 

1,500.0 

1.6 

6.6 

IOO.O 

8.3 

2.8 
IIO.O 

51.0 

5,000.0 

3-3 

650.0 

36.0 

132.0 

15-5 
130.0 
3.68 
62.0 

I  .O 


0.03 

3,800.0 

163.0 

500.0 

6.6 

40.0 

IIO.O 

I2O.O 

29.0 


INTRODUCTION   TO   ORGANIC   CHEMISTRY 


410 


^-Phthalic 

Phenylacetic 

Phenol 

0-Nitrophenol 

m-Nitrophenol 

Dinitrophenol 

Dinitrophenol 

Dinitrophenol 

Picric  acid 

Bases 

Methylamine 
Dimethylamine 
Trimethylamine 
Glycine 
Aniline 
Benzylamine 
Diazoniumhydroxide 


Ammonia 
Boric  acid 
Phosphoric  acid 
Sulphuric  acid 


C6H4(CO.OH)2  i,  4 
C6H6.CH2.CO.OH 
C«H6OH 

C6H4(OH)N02  i,  2 
C,H4(OH)N08  i,  3 
C6H3(OH)(N02)2i,2,4 
C.KUOHXNOOu  i,  2,6 
C6H,(OH)(N02)2  i,  3,  6 
C«H2(OH)(N02), 

CH3NH2 

(CH8)2NH 

(CH3)8N 

CHiNH2.CO.OH 

C6H6NH2 

C6H8.CH2NHa 

C«H6N2OH 


5-3 

0.000013 
o . 006800 
o . 000530 
8.0 

17.4 

0.7 

16,000.0 

50.0 
74.0 

7-4 

0.000018 

0.000046 

2.4 
123.0 

1.8 

0.00006 
900.0 
45,000.0 


BOOKS   FOR   REFERENCE   AND   COLLATERAL  READING 


Books  for  Reference  and  Collateral  Reading 

MEYER  UND  JACOBSON,  Lehrbuch  der  Organischen  Chemie. 

ROSCOE  AND  SCHLORLEMMER,  Organic  Chemistry. 

COHEN,  J.  B.,  Organic  Chemistry  for  Advanced  Students. 

THORPE,  T.  E.,  Dictionary  of  Applied  Chemistry. 

MARTIN,  GEOFFREY,  Industrial  and  Manufacturing  Chemistry;  Organic. 

SroowiCK,  N.  V.,  Organic  Chemistry  of  Nitrogen. 

STEWART,  A.  W.,  Recent  Advances  in  Organic  Chemistry. 

STEWART,  A.  W.,  Stereochemistry. 

KEANE,  C.  A.,  Modern  Organic  Chemistry.     (Stereochemistry  and  Sugars.) 

THOMSEN,  JULIUS,  (Translated  by  Katharine  A.  Burke)  Thermochemistry. 

CAIN  AND  THORPE,  Synthetic  Dyestuffs. 

FOWLER,  G.  J.,  Introduction  to  Bacteriological  and  Enzyme  Chemistry. 

CONHEIM,  OTTO,  Enzymes. 

PLIMMER,  R.  H.  A.,  Chemical  Constitution  of  the  Proteins. 

MATHEWS,  A.  P.,  Physiological  Chemistry. 


INDEX 


Where   more  than    one   reference   is  given,    the   most   important   is   in  heavy  type. 


Acenaphthene,  392 
Acetals,  79 
Acetaldehyde,  77 
Acetamide,  137 
Acetanilide,  306 
Acetates,  96,  100 
Acetic  acid,  94,  98 

electrolysis,  29 

glacial,  96 

structure,  97 
Acetoacetic  acid,  174 

ethyl  esters,  174 
Acetone,  89 

Acetonitrile,  100,  129,  138,  153 
Acetonylacetone,  163 
Acetophenone,  348 
Acetoxime,  79 
Acetyl  chloride,  114 
Acetylene,  47  ...J^»  C  •$.  H  ^ 

series,  42,  45 
Acetylformic  acid,  173 
Acid  anhydrides,  117-119 
table,  117 

bromides,  116 

chlorides,  114 
table,  117 

iodides,  116 
Acids,  activity,  250,  362 

aliphatic,  94,  100,  107 

aromatic,  353-358 
•    dibasic,  177-195 


Acids,  general  properties,  100 
halogen-substituted,  247-251 
hydroxy,     163-173,     182-197, 

36i 
methods  of  formation,  98,  178, 

353 

nomenclature,  102 

tables,  101,  177,  197,  356 

unsaturated,  no,  186,  357 
Acrolem,  86,  159 
Acrose,  85 
Acrylic  acid,  HO 

aldehyde,  86 
Acyl,  114 

halides,  114-117 
Aesculin,  202 
Alanine,  255 
Albumins,  406 
Alcohol- acids,  163 
Alcoholates,  62 
Alcohols,  57 

aromatic,  327,  339 

classification,  65 

formulas,  57 

isomeric,  65,  68 

oxidation,  64,  112,  161 

polyhydric,  155,  157 

primary,  table,  67 

reactions,  62 

unsaturated,  68 
Aldehyde-alcohols,  162 
Aldehyde-ketones,  163 
Aldehyde-resins,  82 


412 


INDEX 


Aldehydes,  aliphatic,  76 

aromatic,  343~347 

condensation,  82,  345 

halogen  derivatives,  91,  247 

polymerization,  81 

reactions  of,  78,  344 

series,  83 

table,  87 

tests,  86 

unsaturated,  86 
Aldol,  82,  162 
Aldoses,  199 
Aldoximes,  79 
Alizarin,  388,  391 
Alkaloids,  402-404 
Alkenes,  44,  47 
Alkyl,  22 

cyanides,  153 

disulphides,  240 

halides,  31,  122 
reactions  of,  33 
tables,  33 

isocyanates,  1540 

isocyanides,  154 

isonitriles,  154 

sulphoxides,  240 
Alkylene  oxides,  157 
Allantoin,  234 
Alloxan,  234 
Allyl  alcohol,  69 

chloride,  55 
Amanitine,  402 
Amides,  137-142,  359 

reactions,  139 

structure,  141 

table,  142 
Amido  group,  127 
Amidol,  338 
Amines,  aliphatic,  127-136 

reactions,  131 

table  of,  136 


Amines,  aromatic,  301 

table,  312 

Aminoacetic  acid,  254,  405 
Amino  acids,  252-256,  360,  405 

alcohols,  251 

aldehydes,  251 

group,  127 
Aminophenols,  338 
Aminopropionic  acid,  255 
Aminoazo  compounds,  317 
Ammonium  carbamate,  229 

cyanate,  150,  231 

thiocyanate,  153 
Amygdalin,  147,  202,  345,  364 
Amyl  alcohols,  67,  170 

table,  68 
Amyloid,  222 
Anethol,  347 
Aniline,  303-306 

derivatives,  306-310 

homologues,  310 
Anisaldehyde,  347 
Anisic  acid,  365 
Anisol,  341 
Anthracene,  282,  388 
Anthranilic  acid,  360 
Anthraquinone,  390 
Antifebrine,  307 
Antipyrine,  307 
Arabinose,  201,  221 
Argol,  189 

Aromatic  acids,  353-3700 
table,  356 

alcohols,  339-341 

aldehydes,  343-348 

amines,  301-312 
table,  312 

ethers,  341 

halogen  compounds,  284-288 
table,  286 

hydrocarbons,  265,  273,  282 


INDEX 


414 


Aromatic  hydrocarbons,  table,  276 
ketones,  348 

nitro  compounds,  293-298 
rules  for  substitution,  299 
sulphonic  acids,  288-292 
table,  292 

Arsines,  136 

Aryl  radicals,  272 

Asparagine,  255 

Aspartic  acid,  255 

Aspirin,  365 

Asymmetric  carbon  atoms,  168 

Atropine,  403 

Azobenzene,  322 

Azo-compounds,  321,  322 
dyes,  325 

Azoxybenzene,  322 

Azoxy-compounds,  322 

B 

Bakelite,  339 
Beer,  61 
Beeswax,  125 
Beet  sugar,  212 
Benzal  chloride,  288 
Benzaldehyde,  344,  345 
Benzamide,  359 
Benzene,  265-272 

derivatives,  isomerism  of,  268 

homologues,  273 

structure,  267-271 
Benzidine,  323 
Benzil,  349 
Benzine,  23 
Benzoic  acid,  355 
Benzoin,  349 

gum,  355 
Benzonitrile,  359 
Benzophenone,  348 
Benzopurpurin,  387 


Benzoquinone,  350 
Benzotrichloride,  288 
Benzoylchloride,  358 
Benzoylglycine,  359 
Benzylalcohol,  340 
Benzylamines,  311 
Benzylchloride,  287 
Betame,  255 
Biuret,  232 

test,  233 
Borneol,  380 
Brandy,  6 1 
Bromacetylene,  55 
Bromalin,  133 
Bromhydrins,  247 
Brucine,  404 
Butadiene,  378 
Butter  fat,  i6oa 
Butyl  alcohols,  65 
Butyric  acids,  108 


Cacodyl,  13? 

Caffeine,  235 

Calcium  cyanamide,  145 

Camphene,  378 

Camphor,  379 

artificial,  377,  380 

Cane-sugar,  211 

Carbamic  acid,  229 

Carbinol,  66 

Carbohydrates,  198 

Carbolic  acid,  328 

Carbon,  detection,  5 
disulphide,  242 
estimation,  8 
oxysulphide,  242 
tetrachloride,  40 

Carbonic  acid,  227 
amides,  229 


415 


INDEX 


Carbonic  acids,  esters,  228 

sulphur  derivatives,  243 
Carbonyl  chloramide,  233 

chloride,  39,  227 

group,  88,  91 
Carboxyl  group,  98 
Carbylamine  reaction,  132,  154 
Carvacrol,  332 
Casein,  407 
Catechol,  333,  366, 
Celluloid,  223 
Cellulose,  221 

nitrates,  223 

triacetate,  223 
Cephalin,  135 
Chavicol,  333 
Chloracetic  acids,  248 
Chloral,  80,  91,  245,  247 

alcoholate,  92 

hydrate,  91 
Chloralcohols,  245 
Chloranil,  352 
Chlorethers,  246 
Chlorination,  31,  284 
Chlorformic  acid,  248 
Chlorhydrins,  47,  156,  246 
Chloroform,  39 
Choline,  134 

Chromophore  groups,  324,  352 
Chrysene,  392 
Cineol,  381 
Cinnamic  acid,  357 

aldehyde,  346 
Cinnamyl  alcohol,  340 
Citral,  87 
Citric  acid,  195 
Coal  tar,  distillation,  266 
Cocaine,  404 
Collodion,  223 
Collogen,  407 
Congo  dyes,  323,  387 


Coniine,  402 
Creatine,  254 
Cresols,  332 
Crotonic  acids,  in 

aldehyde,  87 
Cumene,  278 
Cummic  aldehyde,  346 
Cyanamide,  149 
Cyanic  acid,  149 
Cyanogen,  145 

chloride,  149 

compounds,  144 
Cyanuric  acid,  149 

chloride,  148 
Cyclic  compounds,  257 
Cyclohexane,  373 
Cycloparaffins,  257-261,  373 

stereochemistry,  259 

table  of,  258 
Cymene,  278 


Dextrin,  219,  220 
Dextrose,  202 
Diacetylene,  50 
Diastase,  219 

Diazoamino-compounds,  316 
Diazo  compounds,  305,  313-320 

reactions,  315 

structure,  314,  318 
Diazonium  compounds,  314 
Diazotization,  313 
Dibasic  acids,  table,  177 
Dibenzylbenzene,  282 
Dichloracetone,  93 
Digallic  acid,  367 
Dihydrobenzene,  371 
Dihydroxy acetone,  161,  201' 
Di-olefines,  44,  50 


INDEX 


416 


Diphenyl,  282 

amine,  311 

carbinol,  340,  349 

ether,  341 

ethyl ene,  282 

methane,  349 
Dipropargyl,  50 
Disaccharoses,  211 
Distillation,  fractional,  7,  23 

in  steam,  8 

of  coal  tar,  266 

of  wood,  59 
Bisulphides,  240 
Divinyl  ether,  75 
Dulcitol,  205 
Durene,  278 
Dyes,  323-326 
Dynamite,  160 


E 


Elaidic  acid,  no 

Elementary  analysis,  6,  8 

Energy,  storage  in  plants,  223 

Enzymes,  224 

Eosin,  334,  370 

Erytttfose,  201 

Essential  oils,  160 

Esters,  35,  63,  119,  123 
of  carbonic  acid,  228 
of  inorganic  acids,  119-122 
of  organic  acids,  123,  125 
reactions,  124 
table  of  ethyl,  123 

fitard's  method,  344 

Ethane,  27 

Ether,  70 

Ethereal  salts,  35,  63,  119,  123 

Ethers,  aliphatic,  70 
aromatic,  341 


Ethers,  mixed,  74 

reactions,  72 

table,  75 
Ethoxides,  63 
Ethyl  acetate,  123-125 

alcohol,  60-62 

ether,  70 

hydrogen  sulphate,  120 

malonate,  181 

mercaptan,  238 

nitrite,  122 

propargylether,  75 

sulphate,  120 

sulphuric  acid,  120 
Ethylene,  46,  120 

alcohol,  155,  157 

bromide,  46 

glycol,  155,  157 

oxide,  157 

series,  42,  45 
Ethylidene  chloride,  41 
Eucalyptol,  381 
Eugenol,  342,  347 


Fats,  108,  160 
Patty  acids,  107 
Fenchone,  380 
Fermentation,  60,  224 

acetic,  94 

alcoholic,  60,  224 

butyric,  108 

lactic,  165 

Fittig's  synthesis,  273,  287 
Fluoran,  369 
Fluorene,  392 
Fluorescein,  334,  370 
Formaldehyde,  83 

polymerization,  85 
Formalin,  84 


INDEX 


Formamide,  139 
Formates,  106 
Formic  acid,  102,  178 
Formulas,  empirical,  9 

establishment,  9-12 

molecular,  10 

structural,  12,  1 8 
Friedel  and  Craft's  synthesis,  274, 

348,  349,  354.  389 
Fructose,  204 

inactive,  208 
Fruit  sugar,  204 
Fulminic  acid,  151 
Fumaric  acid,  186 
Furan  and  derivatives,  393 
Fusel  oil,  66 


Galactose,  205 

Gallic  acid,  366 

Gallotannic  acid,  367 

Gasoline,  23 

Gattermann's  reaction,  316,  344 

Geranial,  87,  374 

Geraniol,  87 

Gluconic  acid,  204 

Glucose,  202 

Glucosides,  202,  345 

Glyceric  acid,  172 

Glycerol,  158 

Glyceryl  aldehyde,  201 

trinitrate,  159 
Glycine,  254,  405 
Glycocoll,  254 
Glycogen,  220 
Glycol,  155 
Glycolide,  172 
Gly collie  acid,  161,  163 

aldehyde,  161,  162,  200 
Glycols,  155 


Glyoxal,  161,  163 
Glyoxylic  acid,  161,  173 
Grape-sugar,  202 
Grignard's  reagents,  36 
Grignard's  syntheses,  28,  36,  66, 
81,  89,  96,  99,  274,  287, 

354 

Guaiacol,  333,  342 
Guanidine,  233 
Guanine,  235 
Gums,  221 
Gun-cotton,  223 

H 

Halogen  carriers,  31,  284 

derivatives,     aromatic,     284- 

288 

hydrolysis,  410 
of  acids,  247 
of  aldehydes,  91,  247 
of  ketones,  93,  247 
of  paraffins,  31 
of    unsaturated    hydrocar- 
bons, 54 
tables,  33,  40 
Halogenhydrins,  246 
Halogens,  detection,  6 

estimation,  9 
Heats  of  combustion,  51 

of  formation,  51 

Heterocyclic  compounds,  393-401 
Hexachlorethane,  40 
Hexahydrobenzene,  282,  371 
Hexahydrobenzoic  acid,  355,  375 
Hexahydroxylbenzene,  336 
Hexamethylene,  259,  373 

tetramine,  84,  133 
Hexoses,  201-211 

stereochemistry,  210 
Hippuric  acid,  359 


INDEX 


418 


Hofmann's  reaction,  129,  361 
Hydracrylic,  acid,  171 
Hydramines,  251 
Hydrazines,  317 
Hydrazo-compounds,  322 
Hydrazones,  80,  208,  318 
Hydro-aromatic  compounds,  371 

acids,  375 

Hydrobenzenes,  371 
Hydrocarbons,  aromatic,  265-283 

carbocyclic,  257-261 

halogen  derivatives,  31,  54,  284 

hydro-aromatic,  371,  383 

methane  series,  15 

saturated,  15 

tables,  17,  45,  258 

unsaturated,  42,  50 
Hydrocinnamic  acid,  358 
Hydrocyanic  acid,  147 
Hydrogen,  detection,  6 

estimation,  8 
Hydromellitic  acid,  376 
Hydroquinone,  335 
Hydroxy  acids,  163,  361 

dehydration,  171 

tables,  197,  364 
Hydroxyazo  compounds,  317 
Hydroxylamine,  122 
Hydroxymalonic  acids,  182 
Hydroxypropionic  acids,  164 
Hydroxyquinol,  335 


Indican,  401 

Indigo,  398-401 

dyeing  with,  401 
synthesis,  400 

Indol,  399 

Indoxyl,  361,  400 

Inks,  367 


Tnosite,  373 

Inulin,  220 

Invert  sugar,  202,  204,  214 

Invertase,  224 

lodoacetylene,  55 

lodeosin,  370 

lodoform,  39 

lodohydrins,  247 

lonization  constants,  363,  408 

lonone,  87,  374 

Irone,  374 

Isatin,  398 

Isoborneol,  380 

Isobutyric  acid,  108 

Isocyanic  acid,  148,  151 

Isolinolenic  acid,  112 

Isomerism,  13,  17,  29,  41,  44,  65, 

151,  166,  186,  268 
Isonitriles,  154 
Isophthalic  acid,  368 
Isoprene,  50,  377 
Isoquinoline,  398 
Isosuccinic  acid,  185 
Isothiocyanates,  153 


K 

Kerosene,  24 
Ketocyclohexane,  374 
Ketoles,  162 
Ketoses,  199 
Ketones  aliphatic,  88 

aromatic,  348 

halogen  derivatives,  93 

identification,  91 

mixed,  89 

reactions,  90 

table,  88 
Ketoximes,  80 
Kolbe's  synthesis,  362,  365 


419 


INDEX 


Laboratory  operations,  13 
Lactic  acid,  165,  170,  364 
Lactide,  171,  172 
Lactones,  172 
Lactose,  215 
Lecithins,  134 
Levulose,  204 
Liebermann's  reaction,  131 
Limonene,  378 
Linolenic  acid,  112 
Linolic  acid,  112 
Linseed  oil,  i6oa 
Liquors,  distilled,  61 
Lysine,  255 

M 

Maleic  acid,  186 
Malic  acid,  185,  255 
Malonic  acid,  180 

hydro  xy,  182 

synthesis,  182 
Maltose,  215 
Mandelic  acid,  364 
Mannitol,  205 
Mannose,  205 
Mellitic  acid,  370 
Menthol,  381 
Menthone,  381 
Mercaptans,  238 
Mercaptides,  238 
Mercerized  cotton,  222 
Mercury  thiocyanate,  153 
Mesitylene,  278 
Mesotartaric  acid,  193 
Mesoxalic  acid,  183 
Metaformaldehyde,  85 
Metaldehyde,  82 
Methane,  25 

series,  17 


Methoxides,  63 
Methyl  alcohol,  59 

carbinol,  66 

chloride,  38 

cyanide,  35,  99 

cyclohexane,  373 

glyoxal,  163 

orange,  326 
Methylamines,  132 
Methylene  iodide,  38 
Metol,  339 
Milk  sugar,  215 
Molasses,  212 
Monosaccharoses,  1 99-2 1 1 

synthesis,  206 
Morphine,  404 
Muscarine,  251,  402 
Mustard  oils,  153 

N 

Naphthalene,  282,  382 

derivatives,  384 
Naphthols,  386 
Naphthoquinones,  387 
Naphthylamines,  386 
Neurine,  133 
Nicotine,  403 
Nicotinic  acid,  397,  403 
Nitranilines,  308 
Nitration,  293 
Nitriles,  99,    100,   140,    153,   164, 

178,  290 

Nitrobenzene,    298 
Nitrocelluloses,    223 
Nitro-compounds,  aliphatic,  142 

aromatic,  293-298 

structure,  143,  296 

table,  297 
Nitroform,  143 
Nitrogen,  detection,  6 

estimation,  8 


INDEX 


42O 


Nitroglycerin,  159 

Nitrolime,  145 

Nitroparaffins,  142 

Nitrophenols,  337 

Nomenclature,  22,  44,  63,  65,  83, 
90,  102,  127,  155,  175, 
199,  257,  270,  328 

Novocaine,  310 

O 

Oils,  essential,  160 
hardened,  1606 
natural,  160 
Olefines,  44 
Oleic  acid,  108,  no 
Olein,  i6oa 

Optically    active    substances,    67, 
108,    165,  173,   185,   190, 
192,    201-216,    255,    374, 
378,  379,  408 
Orcin,  334 

Organic  acids,  esters,  123 
Organic  compounds,  i 
characteristics,  i 
classification,  13 
elements  in,  4,  6 
identification,  5 
sources,  3 

Orientation     of     aromatic     com- 
pounds, 280 
Osazones,  208 
Oxalic  acid,  161,  177 

esters  and  salts,  179 
Oxamic  acid,  180 
Oxamide,  146,  180 
Oxidation  of  alcohols,  64,  161 

study,  112 
Oxidizing  agents,  64 
Oximes,  79 
Oxindol,  399 


Palmitic  acid,  108 
Palmitin,  i6oa 
Paraffins,  15 

formation,  28 

halogen  derivatives,  31 

identification,  30 

normal,  table,  17 

occurrence,  22 

polyhalogen  derivatives,  table, 

40 

Paraform,  85 
Paraldehyde,  81 
Parchment  paper,  222 
Pentamethylene,  259 
Pentoses,  201 
Perkin's  reaction,  357 
Petrolatum,  23 
Petroleum,  22 

ether,  23 
Phenacetin,  342 
Phenanthrene,  392 
Phenol,  327-330 

acids,  360 

alcohols,  341 

esters,  339 

homologues,  332 
Phenolphthaleln,  369 
Phenols,  327-339 

derivatives,  336 

esters,  339 

table,  331 

Phenolsulphonic  acids,  337 
Phenyl,  272,  328 

acetic  acid,  357 

acetylene,  279,  358 

carbinol,  340 

glycollic  acid,  364 

hydrazine,  318 

hydrazone,  80,  208 


421 


INDEX 


Phenyl,  hydroxylamine,  321 

propionic  acid,  358 
Phloroglucinol,  335 
Phosgene,  228 
Phosphines,  136 
Phosphorus,  detection,  6 

estimation,  9 
Phthalic  acid,  368 

anhydride,  369,  390,  391 
Phthalide,  370 
Phthalyl  chloride,  370 
Picric  acid,  337 
Pinacones,  90,  349 
Pinene,  376 
Piperidine,  396 
Piperonal,  342 
Piperonylic  acid,  366 
Polycarboxylic  acids,  177,  368 
Polypeptides,  405 
Polysaccharoses,  211-223 
Potassium  cyanate,  146,  150 

cyanide,  144 

ferrocyanide,  144 

thiocyanate,  153 
Propargyl  alcohol,  69 

halides,  55 
Propiolic  acid,  1 1 1 
Propionic  acid,  107 
Propyl  alcohols,  65 
Proteins,  404-407 
Protocatechuic  acid,  365 
Prussic  acid,  147 
Ptomains,  134 
Ptyalin,  219 
Pulegone,  381 

Purification  of  compounds,  7 
Purine  bases,  235 
Purity,  tests,  7 
Pyrene,  392 
Pyridine,  396 
Pyrocatechol,  333 


Pyrogallic  acid,  335 
Pyrogallol,  335 
Pyroligneous  acid,  59,  95 
Pyromellitic  anhydride,  370 
Pyromucic  acid,  394 
Pyroracemic  acid,  173,  190 
Pyrotartaric  acid,  190 
Pyrrol,  395 
Pyruvic  acid,  173 

Q 

Quaternary     ammonium     deriva- 
tives, 128,  135 
Quercite,  373 
Quinic  acid,  335,  350,  375 
Quinine,  404 
Quinoid  group,  324,  352 
Quinol,  335 
Quinoline,  397 
Quinolinic  acid,  397 
Quinone,  307,  350 
Quinones,  349~352 


Racemic  acid,  191 

compounds,  192 

resolution,  192 
Raffinose,  216 
Reducin,  338 
Reference  books,  411 
Reimer-Tiemann  reaction,  347 
Resorcinol,  334 
Rhamnose,  201 
Rochelle  salt,  189 
Rodinal,  338 
Rubber,  artificial,  50,  378 


Sabatier  and  Senderens'  reaction, 

47,  1606,  371 
Saccharic  acid,  204 


INDEX 


422 


Saccharin,  359 
Saccharose,  211 

structure,  214 
Safrol,  342 
Salicyl  alcohol,  341 

aldehyde,  346 
Salicylic  acid,  365 
Saliformin,  133 
Salol,  365 
Salvarsan,  339 
Sandmeyer's    reaction,    316,    359, 

361 

Sarcosine,  254 
Schiff's  reaction,  86,  91 
Schotten-Baumann  reaction,  358 
Silk,  artificial,  222 
Silver  cyanamide,  149 
Soaps,  109 
Sodium  cyanide,  144 
Sorbic  acid,  112 
Sorbitol,  204,  206 
Sorbose,  206 
Specific  rotations,  408 
Spermaceti,  125 
Starch,  218 
Stearic  acid,  108 
Stearin,  109,  i6oa 
Stereochemistry,    166,     186,    193, 

210,  259 

Strain  theory,  259 
Strychnine,  404 
Styrene,  279,  358 
Styrolene,  279 
Substitution,  rules,  299 
Succinamide,  184 
Succinic  acid,  183 

anhydride,  184 

hydroxy,  185,  189 
Succinimide,  184 
Sucrose,  211 
Sugars,  199 


Sulphanilic  acid,  307 
Sulphonal,  240 
Sulphonation,  289 
Sulphones,  240 
Sulphonic  acids,  aliphatic,  241 

aromatic,  288 

chlorides,  290,  291 

table,  292 

Sulphonium,  bases  and  salts,  239 
Sulphoxides,  240 

Sulphur,    compounds    containing, 
236 

detection,  6 

estimation,  9 


Tannic  acids,  tannins,  367 

Tartar  emetic,  190 

Tartaric  acids,  189-195 

Tartronic  acid,  182 

Taurine,  133 

Tautomerism,  175 

Terephthalic  acid,  368 

Terpenes,  50,  376 

Terpinene,  378 

Tetraalkyl  ammonium  hydroxides, 

135 

Tetrachlormethane,  40 
Tetrachlorquinone,  352 
Tetrahydrobenzene,  371 
Tetrahydrobenzoic  acid,  355 
Tetraphenylethane,  282 
Tetrose,  201 
Theine,  235 
Theobromine,  235 
Thio  acids,  240 

alcohols,  238 

aldehydes,  240 

carbonic  acid,  243 

cyanic  acid,  152 


423 


INDEX 


Thio  ethers,  238 

ketones,  240 

urea,  153,  244 
Thiophene,  266,  394 
Thymol,  332 
Toluene,  277 
Toluic  acids,  357 
Toluidines,  310 
Trichloracetal,  92 
Trichloracetone,  93 
Trichlormethane,  39 
Triiodomethane,  39 
Trimethylamine,  38,  132,  213 
Trimethylene,  258 
Triphenylamine,  311 
Triphenylbenzene,  282 
Triphenylcarbinol,  340 
Triphenylmethane,  282 
Trisaccharoses,  216 
Turpentine,  376 
Twitchell's  method,  i6ob 

U 

Unsaturated  compounds,  42,  50, 68, 

86,  no,  133,  1 86 
stereoisomerism,  186 
table  of  hydrocarbons,  45 

Urea,  230 

derivatives,  233 

Urethanes,  233 

Uric  acid,  234 

Urotropin,  133 


Valeric  acid,  108,  170 
Vanillin,  347 
Vaseline,  23 
Veratric  acid,  366 
Vinasse,  213 
Vinegar,  94 
Vinyl  alcohol,  69 

amine,  133 

halides,  55 
Viscose,  222 

W 

Waxes,  composition,  125 
Whiskey,  61 
Wines,  61 
Wood  alcohol,  59 
Wurtz  reaction,  129 

X 

Xanthic  acids,  243 
Xanthine,  235 
Xylan,  221 
Xylenes,  277 
Xylidines,  310 
Xylose,  201,  221 


Zymase,  224 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 


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This  book  is  DUE  on  the  last  date  stamped  below. 


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22Jan'5f/r 

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